The battle system shines when fighting against single opponents, but yeah, some of the bosses don't really care. It's almost like you're playing a turn-based game, waiting for the boss to stop stomping around so you can attack. There's a boss later on in San Fransokyo that does the same exact thing.

Bosses typicaly have a hidden revenge value. Everytime Sora lands an attack he adds to that value and once it reaches a certain number the boss will retaliate with a counter attack. This is to prevent Bosses from being infinte comboed.

For boss fights i recommend throwing out all your combo+ and air combo+.
In fact if you have negative combo put that in. The shorter your combo the faster you get to your finisher which is were the real damage is at. Dont know about KH3 but in KH2 you can even do multiple finisher in a row allowing you at one point to have combos that are just purely made up of finisher moves.

The reasoning is: If the boss is guaranteed to counter on the 4th hit you rather have a 3 piece finisher combo and reposition yourself, then a 10 hit combo which gets broken on hit 4 were youll never get to use the finishers and also eat guaranteed damage from the bosses revenge attack.

The Black Slime.... I can only think you mean the boss in Monstropolis?

That boss takes little damage in its slime form. Most damage comes from the transition where all the hands are around the edge and the big winged thing in the middle.

Dodge roll to the boss, do NOT jump, and begin attacking from the ground. That boss is SUPER bad on critical, because it takes even less damage in its slime form.

Make sure you take advantage of your available Formchanges and store them (switch to another Keyblade to pause the timer.) The final boss of Monstropolis is particularly vulnerable to the finisher with the Ever After Keyblade from Corona.

Take advantage of i-frames and figure out when it's safe to be airborne and when it isn't.

Also, if you're willing to bend the rules a little, I highly recommend trying the Improved Movement mod to feel a little less clunky.

Originally posted by GlitchyReal:

Make sure you take advantage of your available Formchanges and store them (switch to another Keyblade to pause the timer.) The final boss of Monstropolis is particularly vulnerable to the finisher with the Ever After Keyblade from Corona.

Take advantage of i-frames and figure out when it's safe to be airborne and when it isn't.

Also, if you're willing to bend the rules a little, I highly recommend trying the Improved Movement mod to feel a little less clunky.

Sorry, call me stupid, but are you saying magic based attacks and special moves are effective on some bosses/monsters and physical is effective on others?

Yes, some bosses are weak against magic in general or some element of it. I'm pretty sure some of the continue tips (when you die against a boss) will sometimes mention their weakness.

The Monstropolis boss isn't actually weak against Blizzard, he just resists everything else.

Originally posted by Genius Destroyer:

Originally posted by GlitchyReal:

Make sure you take advantage of your available Formchanges and store them (switch to another Keyblade to pause the timer.) The final boss of Monstropolis is particularly vulnerable to the finisher with the Ever After Keyblade from Corona.

Take advantage of i-frames and figure out when it's safe to be airborne and when it isn't.

Also, if you're willing to bend the rules a little, I highly recommend trying the Improved Movement mod to feel a little less clunky.

Sorry, call me stupid, but are you saying magic based attacks and special moves are effective on some bosses/monsters and physical is effective on others?

Its the RPG part of Action RPG.

Although on Normal or under, most of that can be ignored in all of the games.

But on difficulties like Critical or Critical Level 1, it gets more essential.

Originally posted by mdesaleah:

Originally posted by Genius Destroyer:

Sorry, call me stupid, but are you saying magic based attacks and special moves are effective on some bosses/monsters and physical is effective on others?

Its the RPG part of Action RPG.

Although on Normal or under, most of that can be ignored in all of the games.

But on difficulties like Critical or Critical Level 1, it gets more essential.

I'm playing on normal, and the Monstopolis boss was a frustrating fight, so if i knew magic would have been effective, well it would be been less annoying, is there a way to "know" if a monster/boss is weak to magic or physical?
(and why is casting magic so clunky?!)

Originally posted by Genius Destroyer:

Originally posted by mdesaleah:

Its the RPG part of Action RPG.

Although on Normal or under, most of that can be ignored in all of the games.

But on difficulties like Critical or Critical Level 1, it gets more essential.

I'm playing on normal, and the Monstopolis boss was a frustrating fight, so if i knew magic would have been effective, well it would be been less annoying, is there a way to "know" if a monster/boss is weak to magic or physical?
(and why is casting magic so clunky?!)

Testing.

You've played 0.2? Its kind of like that where there are different versions of magic.

Originally posted by Genius Destroyer:

Originally posted by mdesaleah:

Its the RPG part of Action RPG.

Although on Normal or under, most of that can be ignored in all of the games.

But on difficulties like Critical or Critical Level 1, it gets more essential.

I'm playing on normal, and the Monstopolis boss was a frustrating fight, so if i knew magic would have been effective, well it would be been less annoying, is there a way to "know" if a monster/boss is weak to magic or physical?
(and why is casting magic so clunky?!)

The monstropolis fight is one of the game's first real skill checks. Going into it with a mashing X mentality will punish you. Its meant to prepare you for later fights. As for the physical/magic thing you generally want to mix up your combat as the game rewards a more varied playstyle (grand magic casts combined with keyblade form changes can dish out MASSIVE damage). Run in between boss attacks, get a couple combos in, retreat, throw magic at it while you wait for an opening. In case you don't know the free ability MP safety is VERY useful when using magic offensively (it makes sure you never cast a non cure spell when you have less MP than the spell costs, saving your last mp point for cure). Try to take advantage of the side effects of magic (water gives you a dodge roll-like invincibility frame, blizzard makes a rail you can ride to the target, thunder makes the target damage nearby enemies (good for bosses with multiple parts or extra minions)).

Most elemental resistances and weaknesses make sense at a glance (That guy is on fire! maybe water or ice is good?) the monstropolis boss kind of hints at blizzard with all the fire leading up to the boss. A good tactic to pick up early on is carry varied keyblades to adapt to situations. The steam exclusive keyblade is easily the best magic enhancing keyblade but its pretty overpowered and can trivialize the game due to level 4 grand magic one shotting things. In the early game the toy story keyblade combined with the tangled keyblade creates a good variety. You can prepare for a boss by transforming a keyblade then quickly switching to another, you will keep the transform without draining the timer until you switch back to it. This is absolutely a mandatory skill on critical mode.

When all else fails a quick glance at the KH wiki will tell you weaknesses and tips. There were a few gimmicks that made me question the designer's sanity (though more in KH2 than 3).