It seems that there are no guides for this game at all, although some things can be slightly confusing at the beginning (it was for me at least), so I decided to make a brief guide that will cover both achievements and some general information about the game.

If you'll have something to add or know more effective way to achieve a particulat goal, feel free to leave a comment!

5-match
Match five or more gems of the same color in a single match


6-match
Match six or more gems of the same color in a single match

Both of these will unlock naturally. While 5-matches are quite hard to miss, for 6+ matches you might need some hard luck or Wild Gems. Here is the example of 7 match (max is 9 I assume):




Killer Instinct 1
Get a Brutal Combo


Killer Instinct 2
Get a Monster Combo


Killer Instinct 3
Get a Killer Combo

Now these are a bit tricky and I haven't figure the one and only way to get them easily. They are totally luck based; although you can more or less prepare the field for a chain match you can't control which gems appear on the board from above. Here is the list of known combos:

2x - Double combo
3x - Triple combo
4x - Super combo
5x - Hyper combo
6x - Brutal combo
7x - Master combo
8x - Awesome combo
9x - Blaster combo
10x - Monster combo
11x - King combo
12x - Killer combo




Master of Mendra Coast
Get three gold stars in every battle in Mendra Coast


Master of Mendra Bay
Get three gold stars in every battle in Mendra Bay


Master of Mendra Crags
Get three gold stars in every battle in Mendra Crags


Master of Rayburn's Canyon
Get three gold stars in every battle in Rayburn's Canyon


Master of The Boneyard
Get three gold stars in every battle in The Boneyard


Master of Shear Valley
Get three gold stars in every battle in Shear Valley


Master of Agrinji's Pit
Get three gold stars in every battle in Agrinji's Pit


Master of The Shuttered Depths
Get three gold stars in every battle in The Shuttered Depths

Getting three gold stars in a level means a perfect game without any of the four characters dead by the end of the fight. It's important to note that if any of your heroes died but you managed to resurrect them and the fight ended with all four being alive you still get three gold stars (like a true oaf I was restarting the games at first).


Champion of Mendra
Earn three gold stars in every campaign battle

This achievement is still a bit unclear to me. Initially I have unlocked all "Get three stars" achievements, but didn't get this one. I tried repeating Arenas, beating Agrinji, etc, but it still didn't work. Finally I just moved manually (moving to the very last "dot", the purple one, and confirming teleport with Onward button) again from Agrinji's Pit area to Shattered Depths area and it popped up alright.


Historian
Learn about the history of the Old Sorcerers

This achievement requires a visit to a certain location in Boneyard zone. It is a blue dot that tells us about the Enlightenment. Here is the screenshot of Javy standing in the exact spot:




Brute Squad
Unlock all fifteen playable characters in the campaign

You will unlock most of them naturally, but some will require to play certain side battles, so make sure you don't skip any. Total amount to unlock in general is 30, but the second 15 are rescued in the Agrinji's dungeon. Here is the list of the first 15 characters to unlock solely in campaign:

Three in One Blow
Kill three foes with a single attack

Staff of Wind (white item that damages all foes, 4620 on level V) should be the easiest way to unlock this.


Milo's Bane
Slay Milo Randall the Sorcerer


Jaina's Bane
Slay Jaina Randall the Sorcerer

Milo and Randall are the endbosses of the campaign. The battle consists of two waves: first you will need to defeat the Abyssal Lord and on the next wave you will face both Milo and Randall together. Each turn one of them will be invincible and after you kill either of them the second one will ascend and become the Sorcerer Supreme that you will need to defeat in order to win the battle.

Both Sorcerers have low cost but high damage spells, so my strategy was built around the following:

1) Flask of Restoration. This one is crucial; you will need to accumulate 27 green mana before killing the Abyssal Lord. Kylie the Alchemist will be helpful with spawning more green gems after a green match.

2) Brutesword or Flail of Might V. Brutesword is low cost high damage item and Flask of Restoration gives more red mana than any other type. Rugger the Knight is good for this one as he adds bonus damage if you have surplus of red mana. If you've completed the Agrinji Dungeon or at least managed to obtain Flail of Might V using it with Javy the Runelord and Red Manastrike potion is the most imba thing that can happen in this game (providing the enemy spawns Red or Blue special gems of course).

3) Martyr's Blade. This is extremely high damage item (7920 on level V) and if wielded by Lane the Musketeer it becomes a really low cost one (only 6 mana when Lane's ability is maxed).

4) Ring of Insight. Helps a lot by spawning white gems for Martyr's Blade.

So the main idea is to have enough mana at the start of the Wave 2 to one shot one of the twins and then finish his ascended relative. Thus, on the first wave keep amassing green mana (IMPORTANT: Maximum mana of one color a hero can have is 30) untill you have at least 27 (one Flask of Restoration costs 9 mana). Then see if you have enough mana of other colors in order to finish the Abyssal Lord. Then spawn all the Flasks, wait one turn, so that the Flasks will give you the mana immediately at the beginning of the Wave 2 and finish the Lord. On the Wave 2 use the most cost efficient weapon to one shot the twin without a shield or make several matches if you see a good possibilities (like 5-match or just a lot of red / white mana). IMPORTANT: You do not lose accumulated mana after one of the twins ascends unlike you do between the normal waves. Having all set, use all of your might to defeat the Sorcerer Supreme and it's gg.


Simultaneity
Slay the Randall twins simultaneously, preventing either of them from ascending to Sorcererhood

Now for the interesting part. Technically you can defeat both twins at once, which will make the fight much easier and shorter, but it requires the following:

1) Good portion of luck

2) Good AOE damage item like Staff of the Wind, Poleaxe or Coronal Lens.

3) Matching the special black gem that makes one of them invincible AND keeping your turn at the same time. If you simply match black special gem and end your turn, the shield will be back again. Keeping your turn can be achieved via 5+ match or any destruction item placed on Wave 1 that will luckily position itself near the special gem and will damage it at the start of your turn forcing it to relocate and leaving both twins vulnerable.

Here is the video to illustrate the strategy. It is quite short because I've got maxed items and characters; RNG was quite generous as well:



Defender of Mendra
Triumph over the Unearth invasion of Mendra

Simply defeat Milo / Jaina (or both, see Simultaneity achievement).


Defender of Mendra... plus.
Triumph over the Unearth invasion of Mendra in Campaign Plus mode

Defeat Milo / Jaina (or both, see Simultaneity achievement) in the Campaign Plus mode, which is unlocked after you beat the standard campaign. Can't say this is any difficult, just a massive RNG with items.


Brute Squad
Defeat the final boss with a full party of Strength characters


Brainy Bunch
Defeat the final boss with a full party of Intelligence characters


Mob Wisdom
Defeat the final boss with a full party of Wisdom characters


Artful Dodgers
Defeat the final boss with a full party of Dexterity characters


Surplus Leadership
Defeat the final boss with a full party of Charisma characters


All Tanks
Defeat the final boss with a full party of Constitution characters

All of these can be effectively completed using the strategy from Simultaneity achievement, just bring the necessary items and match wisely. It's important to note that the attribute (or simply put -
a color) can be either a primary or a secondary stat. Here is another video example of the mentioned strategy using all purple characters (the start wasn't so great, because of the lack of green gems, but it was still doable). Moreover I managed to bring down the shield on the Wave 2 and almost got the twins simultaneously even without AOE weapon =]

Technically Agrinji's Dungeon and Roguelike mode are the same, with Agrinji being a "light" version of this mode. So this section will be covering the (let's call it) Dungeon mode in general with pointing out main differences.


- Agrinji's Dungeon is available after you beat the endgame boss. Four more purple dots will appear to the right of the Randall Twin's red dot so just follow to the last one and press Investigate button as usual.

- Roguelike is available in the main menu from the very start, but I'd strongly recommend to finish the main game first, because Legendary items unlocked there become available in the Roguelike as well.


- You start Agrinji with every unlocked (and rescued from Agrinji) hero at the currently reached level (max is 120, which should be bought by the time you make it here). You also have all the items (inlcuding level V items that are found only in Agrinji) and potions unlocked.

- You start Rogulike with only 4 heroes at level 1 no matter how many you've rescued in your previous Roguelike run. You have only several basic items always at level I no matter how many items of what levels you've unlocked on your previous Roguelike run. Several notes here:

• On the very first run Knuckles the Oaf, Vick the Thief, Steyn the Assassin and Schwann the Cleric are your starting heroes. Later if you unlock more heroes and will be defeated you would be able to pick your starting four from the list of champions you've managed to rescue. So pick wisely, because everyone else from the list will be removed and you will have to rescue them again if you need them for your setup.
  
• Completing main game and Agrinji before starting the Rogulike can help a lot, because legendary items (although level I) and potions (except Stalker's Brew from the very first arena; the reason is unknown) will be available. Dragonbile Vial that grants 8 black mana at the start of the wave was a real lifesaver. Here is the example of your starting screen, notice the items with golden border, those are legendary items unlocked in the main game:

I'm sure this is not the only viable setup, but it beats the crap out of enemies, so I've used it to snowball through Agrinji as well as complete Roguelike. In the latter I had to rescue the certain heroes first and couple of times I just used Give Up button as soon as I found the one I need in order to start with him from the very beginning, but it didn't affect the final results much I think. Please note that I didn't reach level V items by the time I finished the Roguelike, but even items level III - IV worked alright. I did manage to level up my heroes' unique abilities though, because Javi the Runelord gives only 1 mana at first, which is nothing of course.



Javy the Runelord when maxed has this awesome ability to give 4 (!) mana of every (!!) color when matching an enemy red or blue gem. In my setup only red gems matter, because blue is occupied by another hero. Flail of Might V does not end turn when used, so these guys were made for each other. The second item does not matter much, I used Monocle of Insight mostly; it has decent AoE damage, but can destroy your own gems as well, so use with caution.



I find Gray the High Marshall to be very helpful in tough situations because he beefs up your party HP up to 50%, which will help to withstand more damage from enemies that are 20+ levels higher (although you still should try your best not to get your party damaged at all). He can also wield a Brutesword, so that you can finish up an enemy with it, spawn +4 red gem and then match it with Flail if Might V to get even more red mana. The purple item doesn't matter much, I prefer Thunder Badge in Agrinji and Meme Spike in Roguelike.



Watts the Master Healer is my main choice for the health and safety of my party. She heals the whole crew whenever she uses an item for the amount equal of 4% per spent mana point, so if your party have been severely damaged and you have just one opponent left, don't kill him right away (unless it's a hero ofc) but see if you can match more green or blue gems to heal. Ring of Insight (6 mana = 24% HP Heal per use) is a total must to get as much white mana as possible, while Poisoned Ham is a decent damage item with medium mana cost. You can swap the Poisoned Ham for Boots of Vigor if your last fight didn't end up very well and you really need to heal your party asap. Flask of Restoration might also be an option, but I usually went with damage from Ham. All of these items cost 9 mana (36% HP heal per use) by the way, which I consider to be more or less optimal to heal my lads through.



Lane the Musketeer Lord and Martyr's Blade were made for each other just like Javy and the Flail. Martyr's Blade has extremely high damage and initial cost of 9 white mana. Lane's unique ability (when maxed) drops that cost to a mere 6 mana, which is almost nothing for a whooping 7920 punch in da face. Moreover, killing blow spawns a +5 white gem, so with some luck and / or a help of Ring of Insight from Watts this guy becomes the match-3 Apocalypse. The second item doesn't matter that much; I kept Dart Trap Kit in Agrinji and Murderblade in Roguelike.

UPD: After some additional testing I can recommend Staff of Wind as well (instead of Martyr's Blade). It does less damage and spawns only +2 White gem, but to my experience it drastically increases the speed of completing Agrinji because you annihilate the full team instead of 1 enemy. And even if their health is above damage threshold you'll usually have enough mana to finish them with other items.



Now for the potions. Since my setup is based on heavy usage of Red and White mana I pick Manastrike (gives 4 additonal red / white mana on critical match, which is any 4+ match) potions of corresponding color. In the Roguelike, where only legendary potions are available from the start, Dragonbile Vial is strongly recommended with anything else being a second potion untill you find White Manastrike potion.

Both Agrinji and Roguelike are the same in terms of progress mechanics. There are a total of 8 levels, each consisting of up to 20 floors. Each floor will have two battles to choose from with a certain reward available. The last battle on floors 1-7 will have a tough enemy setup or a mini-boss that will guard a Boss Chest. The last battle on floor 8 is the final boss encounter. If your party is defeated at any moment, you either choose another four heroes from the remaining roster and continue or restart from the very first floor if there are no more heroes left available (technically you can play a battle with less than four heroes, just fyi).

Here are possible rewards after the battle:

Captured Hero. This cage adds one random hero to your roster. Permanently in Agrinji, so they won't appear anymore after you've rescued all 30 of them. Temporarily in Roguelike, till the end of run; thus after being defeated you will start with only 4 heroes again.

Normal Chest. Important in the Agrinji untill you get the necessary items upgraded up to level V. Crucial in Roguelike where every fresh run starts with just a few items all at level I. This chest may contain a new item, a higher level item, a potion or a magic crystal that will upgrade your hero's unique ability to the next level.

Boss Chest. It is available at every final encounter on the current floor (except floor 8) and is usually heavily guarded by some high HP / high DMG mobs or even a mini-boss. Frankly I haven't noticed any obvious differences between the contens of Normal and Boss chests, but I do always go for a Boss one anyway.

Gold. Useless in Agrinji. Important in Roguelike where every fresh run starts with level 1 heroes. Thus, you'll definately need some gold to level up your party. You do get some coins by simply completing a battle, but usually it's a really small amount, while these sacks normally yield around 1/2 - 1/3 gold required for a level up.

Magic Star. This reward is available on every third floor on the level (3,6,9, etc). By collecting three Magic Stars you proceed to the next level of the Dungeon (skipping all other floors and receiving some extra gold or loot). Crucial in Agrinji after you've got the items you need. I never picked it up in Roguelike, items and gold are more important.

Healing Fountain. This fountain restores all your champions roster to full HP, both your current four and everyone in the reserve. I never touch it on purpose in Agrinji. Might be useful in Roguelike after an unlucky battle, where you've been severely damaged and didn't have time to heal.

Resurrection Fountain. Allows the resurrection of ONE (and only one) fallen hero from your roster, thankfully you have an option to pick which one. Thus, if you have been defeated once, you'll have to choose four Resurrection Fountains in order to bring everyone back.

Now some choices to make out of two battles on the floor. Please take note that the battle may be against either 4 high level or 8 medium level enemies, so you might take the one with 8 lower HP baddies depending on your current party situation. I personally never looked on the amount of enemies, just chose the item and start the fight.

- In Agrinji I picked every Captured Heroes until all 30 of them have been rescued. Then I focused on Chests and after everyone have been rescued, their unique abilities maxed up and items upgraded to level V Magic Stars became my first priority to reach the final boss as fast as possible.

- Roguelike is a bit more complicated, because things you unlock stay that way only during the current run. If you are defeated everything gets back to zero. Taking into consideration I didn't want to repeat Roguelike twice, because I did want to unlock both Roguelike achievements in one run my priorities were the following. Whenever I see a Captured Hero I pick him till I rescue all 30 good (sort of) guys. If there are no Captured Heroes on the floor I always pick a Chest. Items are crucial, because you might be lacking levels or HP, but a difference between 250 and 4000 damage from a Brutesword + lower mana cost = Roguelike win. If there are no Captured Hero or Chests I always pick Gold to level up my raiding party. I never pick Magic Stars, completing every level of the Dungeon thoroughly and beating the guys guarding the Boss Chest.

And finally the achievements unlocked playing the Dungeon mode:


Agrinji's Bane
Complete Agrinji's Dungeon

Survive all 8 levels of the Agrinji's and beat the final boss.


Oafmaster
Escape alive from the Dungeon of the Dark God!

Survive all 8 levels of the Roguelike mode and beat the final boss. My strategy and tips are available above, so here is the video of the final boss in Agrinji. Please note that this was my first run in Agrinji, so some of my champions are "dead" and I've just decided to try Javy with a bunch of other guys and it turned out that he totally rocks:



Roguelike Rescuer
Unlock all thirty playable characters in a roguelike game

To my experience it is totally possible to unlock all 30 characters and complete the Roguelike mode in one go. A certain number of Chests and Gold will be skipped in favor of Captured Heroes, but it is still doable (at least with my setup). Here is the final screenshot of my party in Rogulike; you can see all 30 champions and my active four being level 61 with some items being only level III (including Flail of Might). They did the job just fine.

Gladiator
Discover the legendary item hidden within each zone's arena battle

One might wonder what is this achievement doing in Agrinji and Roguelike section. Well, as for the moment this achievement is notorious for being reported as broken, because people on forums reported that they have sucessfully unlocked all the legendary items in all of the Arena's and it still won't unlock.

I have a theory that the criteria might be a bit misleading. There are 7 zones each having a green dot that gives out the Arena quest and red dot without stars representing the Arena itself. There is only one legendary item available per zone (Arena) that will randomly spawn after Wave 20, you match that item and can safely leave. Now, my theory is that the Agrinji's Dungeon is considered to be an Arena of the final (8th) zone and one must grab all available legendaries there. As for the moment I'm still working on the items, because it is extremely tedious and exhausting to complete all 8 levels (even with grabbing all Magic Stars on the way) over and over again, but everytime the final boss is defeated I'm being rewarde with ONE new legendary item / potion. So my best hopes are that after I've unlocked all of them this achievement will be finally dealt with. Time will show, so here is the full map and list of legendary items I've discovered in the game so far:



IMPORTANT: All legendary items occupy TWO item slots, so if, for example, you have a hero that can yield a blue and yellow item, equipping him with blue legendary item will disable the yellow item slot. Potions work normally, you can still equip both.


Stalker's Brew
Location: Southern Mendra Coast Arena (after wave 20)

All critical matches and wild gems grant one black mana.


Warlord's Maul
Location: Mendra Bay Arena (after wave 20)

A mighty blow destroys up to three enemy special gems and deals 3200 damage to the owner of each gem destroyed.
Default cost: 10 Red mana.


Fiend's Whip
Location: Mendra Crags Arena (after wave 20)

Lashes a single target dealing 4000 damage. Consumes all intervening (a line is formed between the hero who used it and the target) gems, earning mana for each.
Default cost: 10 Yellow mana.


Plaguelord's Charm
Location: Rayburn's Canyon Arena (after wave 20)

For each dead for transforms a green gem into a Corpse Gem that explodes after two turns, dealing an average of 1600 damage to all foes. Corpse Gems created from mightier foes cause more damage.
Defaul cost: 6 Green mana.


Sky Drake's Fang
Location: Boneyard Arena (after wave 20)

Transforms a random white gem into an eight-turn Spirit Minion Gem. Every turn the Spirit Minion Gem will seek out matches for its master.
Default cost: 9 White mana.


Staff of Storms
Location: Shear Valley Arena (after wave 20)

Transforms two blue gems in Lightning Gems that go off after two turns, consuming all Lightning Gems on the board and destroying gems between them.
Default cost: 6 Blue mana.


Rod of Dissolution
Location: Agrinji's Pit Arena (after wave 20)

Transforms a purple gem into a Chaos Sphere that moves towards its target, consuming all in its path. Deals 2400 damage to the target and any adjacent companions.
Default cost: 10 Purple mana.


Dragonbile Vial
Location: Agrinji's Dungeon (random from the final boss)

Grants 8 black mana at the start of each wave.


Draconic Heartstring
Location: Agrinji's Dungeon (random from the final boss)

Curses the entire enemy team for four turns. Cursed foes take double damage.
Default cost: 10 Red mana.


Dragonshield
Location: Agrinji's Dungeon (random from the final boss)

Blesses the entire party with ivulnerability for one turn.
Default cost: 10 Green mana.


Wyrmbone Staff
Location: Agrinji's Dungeon (random from the final boss)

All white gems consume a neighbor, dealing damage and granting mana.
Default cost: 10 White mana.


Manastorm Wyrmfang
Location: Agrinji's Dungeon (random from the final boss)

Stab a single target, executing it if it's below 20% health, otherwise dealing 10% of its maximum health in damage. Slain targets erupt into a fountain of multicolored mana (not mana, but gems, +X Red gem, +X White gem, Wild gem etc).
Default cost: 10 Purple mana.


Drakeclaw Snare Kit
Location: Agrinji's Dungeon (random from the final boss)

Traps three gems. When a trapped gem is matched, it consumes any adjacent special gems.
Default cost: 4 Yellow mana.


Wyrmspirit Phylactery
Location: Agrinji's Dungeon (random from the final boss)

Immediately matches all ressurection gems on the board.
Default cost: 10 Blue mana.


To be continued as i complete another run (or not if i melt from boredom first) ... Oh my gosh, so much time wasted on this theory and I didn't get the achievement X_X My next best guess is that maybe you need to complete all Arenas in the Campaign Plus as well, so I'll be working on that. At least I got the list of items.

- When matching, enemy gems add to your mana pool, but wild gems do not.
- Don't forget to visit back arena quest giver after getting to wave 20 to receive some extra cash as a reward.
- Simultaniety achievement does not give separate kills achievements, because the latter requires a twin to ascend.
- Poleaxe doesn't seem to be working. It says "allows matches to do full damage to back row targets", but the damage is still halved when matching Red gems with a corresponding strength hero.
- Flask of Restoration V has a typo in description. It says "transforms two green gems", while in fact it transforms three of them.
- Dart Trap Kit seems to drive enemies crazy, because as soon as you pop it, they match it immediately and kill themselves or their teammates and moreover get an extra move for the kill! I assume it's just their AI logic that tries to remove your special gems from the board asap, so you might abuse that if you'd like. I've also noticed that 4+ matches are at the higher AI priority then special gems, so place those wisely.
- Potions do not work on dead-then-resurrected-at-the-same board heroes. So, for example, if Javy has been defeated and you matched his gem to bring him back he won't be affected by Red Manastrike potion (and any other potions) till the end of the battle.
- You can restart the battle (especially in Roguelike) if it went totally south, by "killing" the Oafmatch.exe process in Windows. Game autosaves each battle, so you will start from the very same battle. This might be considered as cheating, but I found it close to impossible to start EVERYTHING from scratch only because the game gave me the worst RNG for 1 battle out of 100. I did use this method couple of times and always completely destroy my enemies on the second try, because RNG dice was simply not the worst; mediocre RNG still works for my build.

I'll be adding anything else i've noticed till I'll 100% the game.

I do like match-3 games with some twist like simple RPG, building, managing and other elements. I've got Oafmatch just out of curiosity and really liked it (till the achievement grinding part, duh). It has this party of four champions + 6 color of gems / items mechanics that doesn't matter much in the beginning, but you'll have to think of a proper setup for the endgame stuff. And the humorous writing of course, it's very well done to my mind and adds a smile every now and then (with Knuckles and Schwann playing the key role).

Judging by the numbers It appears that Oafmatch is mostly overlooked by players and all these poor souls are missing a really nice game for a ridiculously low (even default) price. Maybe some additional advertising could've helped aside from a simple price drop on sale, but well, probably too late for that anyway.

Finally, when you are looking for a fix to any issue, remember the wise words of Knuckles the Oafmaster: