Alien Swarm can be likened as a top-down version of Left 4 Dead (also by Valve), with the addition of class specific skills and objectives that you must complete as you progress through the map. It was first released as a UT2004 mod in 2004, then remade for Source in 2010.

Alien Swarm: Reactive Drop is a fan-made compilation of maps and updates to the 2010 game, made in response to a lack of official updates and map campaigns.

This manual covers a number of basics that should help you figure out where to start, and also contains a number of tips that describe some strategies and easy-to-miss/poorly explained features. To skip to those, just look for lines marked as "Tip".

Daily statistics and speedrun leaderboards are here.[reactive-drop-stats.appspot.com]

The best part of any new game is discovering all the new things for yourself, with trial and error.

Even though I am writing this guide, and you probably have your reasons for reading this, I do encourage you to keep this in mind.

Jacob's Rest is the official campaign designed by Valve, and the first two maps are designed to give you space to learn most of the required controls. The game will provide in-game pop-ups during this process.

If the in-game pop-ups are missing, you can reset it by going to Options>Game Settings, and turning the Game Instructor off and on again.

If you want to do it online, look for lobbies with the Landing Bay and Cargo Elevator maps, which are the names of the first two maps of Jacob's Rest.

Tip: Jumping straight into other maps and/or campaigns without doing Jacob's Rest is not a good idea, as they often assume that you already know about the trickier enemies, and/or they have non-linear map layouts.

As a 4-player co-op game, you'll most often be playing this online. You can choose to either join someone else's game, or create your own.

8-player games have also been enabled for Reactive Drop. However, this was not the intended design for the original Alien Swarm game, so it may feel a little crowded at times.

If you choose to join a Public Game, you should open the Advanced Settings and expand your search region, as the player base for Alien Swarm may be rather small. Alternatively, you can use the old-fashioned dedicated server browser.

If you want to Create a Game, this also means that you are hosting it on a temporary server on your computer. If your internet connection can't handle it, then you may suffer from lag and stuttering when you have too many players and aliens on the map.

Tip: After joining a game, press F9 to view the player list and everyone's ping. You can also vote kick and vote a new leader on this screen.

Tip 2: The maximum size of a game is either four, or eight. Any lobby you see with a higher capacity may be an incorrectly configured server, and you won't be able to join.

Tip 3: If you created the game yourself, choosing to quit means that your server will close, and kick everyone off. There isn't much point in switching to a new leader, and you can't change who's hosting it.

Before the game can begin, you will start in a lobby, where you are required to select a character. Here, you can also change your equipment loadout, and review the map objectives.

Much like any other online game with a preparation lobby, you should click the Ready button to tell the host that you're ready to play.

Tip: If you're trying to select an available character and it refuses to register, there are three possible reasons for it:

• Someone from the previous game has already selected it, but they haven't finished loading the map on their end.
  
• Someone disconnected or timed out. There is a 30 second grace period.
  
• Someone added a Bot player. Bots also count towards the limit of a 4-player game. Tell them to remove it.

It's probably easier if you go into the Keyboard Options to see the entire list. It's similar to a first-person shooter.

There are no mouse settings of any kind, because you are actually just aiming with your on-screen cursor.

That said, here are the attack buttons:

• Fire: Left click.
  
• Alt-fire: Middle click or F key. Not all weapons have this.
  
• Melee: Right click.
  
• Item: 1 key.

Since you already have alt-fire on your middle mouse button, I suggest you rebind your Item key from the 1 key, to the F key.

Tip: By default, you will shoot in a straight line, but some aliens will be above or below you in elevation. To shoot at a very sharp angle of height, place your cursor directly over the target, or leave it to someone who has Auto-Aim enabled.

Tip 2: The 2-8 keys are for controlling the items on your squad members if they are bots, but if it's a player, pressing their key will emote for ammo or healing.


Controller input must first be enabled in the Options menu.

The mouse cursor will stay at a fixed distance from your character, in a circle.

Tip: The default gamepad controls are not well optimised, and is missing the keys for multiplayer communication. It can't be easily changed, so you should go into Steam Big Picture and set a custom Gamepad -> Keyboard configuration.

There are four classes in Alien Swarm, each with their own unique weapons, bonuses, and abilities that assist the team. Each character also has a different stat distribution that leans towards a particular playstyle.

An all-rounder that has high health, and assists the team by simply being present. They are also suited for throwing grenades with various tactical options.

• Unique Weapon: The Vindicator is a unique shotgun with the highest alpha damage in the game. Incendiary Mines that create a wall of fire are an unlockable.
  
• Unique Bonus: Grenade/Explosive Damage is increased.
  
• Unique Ability: Leadership increases the chance of a critical hit and critical save for all nearby players.

Tip: The Officer helps the team by simply staying close to them. Everyone that you keep close to you (ie. on-screen) will recieve the damage/defence bonus. It's a good choice if you are new, or don't want to deal with anything but shooting at bugs and making them explode.

A damage-dealer with lots and lots of bullets, and Auto-Aim. Help the team with more bullets, and shooting at the more difficult enemies.

• Unique Weapon: The Autogun is a machine gun with a high magazine capacity, and Auto-Aim. The faster-firing Minigun is an unlockable.
  
• Unique Bonus: More bullets.
  
• Unique Ability: Piercing Shot. All of your bullets will pass through an alien and hit the one behind it.

Tip: To get more bullets for your Autogun, look for a unique Autogun ammo pickup, first. Most weapons will take 10% or 20% from a generic Ammo Box's supply, but an Autogun requires the entire box. Don't take it unless you think it's okay with everyone else.

The only class that can heal other people – without a Medic, your only alternative is a single-use medkit that takes up your item slot. Help the team by healing them, and not getting yourself killed.

• Unique WeaponItem: The Heal Beacon is placed on the ground, and heals everyone standing inside the circle. The unlockable Medigun allows you to heal on the move. Both items take up a weapon slot.
  
• Unique Bonus: Faith can cure infestation faster, whilst Bastille increases the duration of the Adrenaline item.
  
• Unique Ability: You can heal. That's plenty enough.

Tip: Heal Beacons contain a fixed amount of HP, and fade away after a time, so make sure you don't waste it! Each beacon will heal roughly 80-100% of a life bar if used on a single person, and is divided evenly when there are more people.

The Technical Specialist is the only class that can interact with certain objectives, locking them into a small hacking minigame/puzzle. They're helpless while this is taking place.

• Unique Weapon: The P-Rifle is almost identical to the Assault Rifle, except that it also has Auto-Aim, and fires a different grenade. It's not as impressive as the Autogun, but it's enough to give you a better edge.
  
• Unique Bonus: Fast Building. Techs can weld doors and set up sentry turrets at greater speeds.
  
• Unique Ability: Movement Scanner. Techs will regularly ping your minimap, highlighting the location of enemies nearby.

Tip 1: The pipes/wiring minigame is solved by linking one end of the node, to the other. If you have trouble with a big puzzle, try doing some of it from the opposite end, and then link it in the middle.

Tip 2: The conveyer belt/1's minigame is solved by flipping the switches at the bottom to make all the 1's line up and move in the same direction. Just work on it from left to right.

Instead of playing a single map, completing one mission will link you to another map, as part of a campaign. Completing a map will reward you with ~1000 experience points, which is usually enough to gain a full level. (You will still get some experience if you fail, but did an objective.)

With the exception of one map, Jacob's Rest is mostly linear, so you shouldn't get lost. Williams, your pilot and commanding officer, will also have voice acted segments telling you of your next objective, and giving a bit of story. There are a total of seven missions.

Eight new campaigns and three standalone bonus missions are included in Reactive Drop, which brings a total of 38 new missions to Alien Swarm.

These unofficial campaigns are typically designed to be more difficult and/or non-linear, with features such as more dark areas, smaller corridors, or attacks from multiple angles. There may be some clipped segments of Williams' dialogue that direct you, but you are otherwise required to read the Map/Objective screen.

Some maps also have a mandatory requirement before the game can be started. This is most often someone playing a Tech, and the mission will immediately fail if they die before doing all Tech-required objectives.

The Flamethrower weapon may also be a mandatory requirement. If you have not unlocked this yet, it will be temporarily unlocked for that mission only.

Tip: You can also draw directly on the map, and it will temporarily show up on the mini-map. Use this to figure out where to go. Spectators and dead players can also draw and communicate.

There are five default difficulty levels in Alien Swarm: Easy, Normal, Hard, Insane, and Brutal.

The general strategy for a map is the same across Easy, Normal, and some Hard maps, except that there are increased spawns of aliens, and higher health and damage.

Strategies may change radically on other Hard maps, Insane, and Brutal, as the increased damage and spawn rate becomes overwhelming. Late-game enemies may also appear early.

In addition, playing with 8 people instead of 4 will double the aliens' spawn rate, regardless of setting.

Tip: Brutal was added later on in the original Alien Swarm game, and couldn't actually be completed by the game developers and testers. Oddly enough, the victory statistics are better than on Insane...

Additional modes that work separately from the map's difficulty setting can be set.

• Onslaught removes the resting time between alien spawns, leaving you with no time to heal and recover.
  
• Friendly Fire can be set to Hardcore, which disables all damage reduction. (Friendly fire is always on, but at a reduced rate.)
  
• Challenge will add a modification of your choice to the map. Difficulty Tier will raise your difficulty level to Brutal+ or higher, Level One locks everything but your level 1 weapons, etc.

Tip: The damage reduction from friendly fire is also negated if you don't stop shooting them! A single mistake is okay, but ignoring it in an intense situation will quickly kill them!

One basic formation is to have an Officer taking point, Special Weapons behind them, followed by the Medic, and the Tech watching the rear.

• The Officer's Vindicator has enough alpha damage to take care of any single enemies, and they have extra HP to survive any surprise attacks without dying.
  
• Special Weapons is right behind them to take care of the large groups, but they don't have as much HP.
  
• The Medic is in the middle to easily access everyone, since the Heal Beacon radiates a circle.
  
• The Tech's P-Rifle is weaker than the Autogun, but it's enough to cover the rear or provide backup. Some attacks can still come from behind, so one person should always watch it.

However, this is only a basic example, and anyone can assist in any position as long as they do not forget that their class still has a basic role. Techs still need to move toward the Tech-only objectives, and Medics need to back off and remember to heal people.

Above all else, you should stick together and watch over each other. Don't charge in ahead, or allow yourself to be left behind.

Tip: Even with a fast reload, reloading your weapon will always slow your movement and prevent you from defending yourself. Don't be afraid to back off when this happens, and allow someone else to step in.

Friendly fire is always enabled, so you should always take care that you don't kill each other. Small mistakes are okay, but you shouldn't walk into someone else's line of fire.

Almost every weapon will have a laser pointer and visible tracer bullets, so you'll always know where not to walk.

Some enemies will require concentrated fire, especially on higher difficulty levels, so it's also important that you leave a gap for someone to stand next to you, or shoot past you. You don't always need to stand in the middle of a hallway to shoot. Try to stick to the side!

Tip: Don't waste ammo! Reloading is done by throwing away and replacing the entire magazine, instead of restocking individual bullets. Ammo pickups also give you one magazine at a time.

After gaining a new level, you will unlock a new weapon or item.

Many of the weapons and items unlocked in the game are balanced so that they are not necessarily more powerful than the ones at the lower levels. Most are situational, or fit a particular playstyle.

Each class also has a unique weapon already available to them at level 1, and they also get a strong bonus for their unique weapon. Regardless of your level, you should usually keep this as your primary equip.

On higher difficulties, such as some Hard maps, Insane, and Brutal, the minimum recommended level is either level 9, or level 13.

Often found on maps, the Healkit allows you to heal yourself, exactly once. You shouldn't carry this with you unless you don't have a medic, since they can be found during the mission.

Used to seal and reinforce doors, this prevents aliens from going through and killing you... at least until the door collapses. When it does collapse, you will most often be killed by the door itself, so stand back.

Certain areas of the map are deliberately dark. Unless you want to cheat with your brightness settings, these become useful on the more advanced maps. They also temporarily enable Auto-Aim for everything nearby.

Putting this down will look similar to a Heal Beacon, but this actually doubles your attack damage. It's important for conserving ammo and killing aliens quickly when you need to defend a location.

This will temporarily freeze all aliens that are hit by the grenade, which allows you to get out of a situation where you are swarmed by aliens, and have no backup.

The healing capacity on the Medigun is slightly lower than the Heal Beacon, but you can use it in smaller bursts, and on the move. You can only heal one person at a time, however, and you can't shoot at aliens while using it.

This slows down time. Your fire rate will also be slowed, but this will give you time to prioritise and aim at the right aliens.

This is required for dealing with certain map objectives, and killing a particular alien with minimal risk. Alt-fire is a fire extinguisher, and sustained friendly fire will set your allies on fire.

Tip: The maximum level is 31. When you reach that level, you can select "Promote" to reset your level back to 1 and lose everything. You get a neat badge that counts how many times you did this, but there's no other benefit.

Bot-controlled squad members can be used in both single player and multiplayer, and controlled with various keys.

Select additional characters in the three extra player slots. There won't be a bot if you don't choose a character.

If you want to play in a squad of 8, play in multiplayer mode and set your game to friends-only.

While you are on the prep screen, press the on-screen "+" button below your character's portrait to add a bot. These bots will be owned by you, which is indicated by your avatar.

To unselect your character and remove all of your owned bots, press the "-" button next to it. You should do this to ensure that other players can select a character.

• F1-F8: Switch player control
  
• 2-8 keys: Command: Use a bot's item
  
• Shift+2-8 keys: Use a bot's second item (if equipped)
  
• X: Command: Hold Position
  
• V: Command: Follow Me

When switching from one character to another, the new bot will default to holding its current position. You'll need to send another "Follow Me" command.

Tip: If you have died, or joined mid-game and there is a bot present, you can left click to control the next available bot. To control a specific bot, use the F2-F8 keys to spectate a specific squad member, then left click when watching a bot.

Tip 2: There are separate key bindings for "Follow Me" and "Hold Position", but you can also use the Radio radial menu and use the same two prompts to command them.

These are some hidden settings that are not considered to be cheats. To enable the developer console, toggle it in the keyboard bindings screen, then access it by pressing the ~ key.

The Adrenaline music that is played during a set-piece moment can be replaced. Go to Options>Audio>Customize Combat Music.

This does not alter the music played when using the actual Adrenaline item.

Song files should ideally be a 320kbps mp3 file with all of the ID3 metadata stripped. If you're cutting this in Audacity, just click "Clear".

For reference, the original Adrenaline music is 60 seconds long.

Whether it's for speedruns or survival, here are some extra tips for when you are moving on to higher difficulties or other map campaigns.

A fast reload is done by pressing the reload button again, when the reload bar is being shown. Succeeding will halve your reload time, but failing will double it. Because of both lag and the time penalty, it's better to try to hit it early.

Aliens can also be burned, frozen, shocked, or exploded. Explosions have high damage and friendly fire. Freezing won't damage, but will fully stun. Stun/Shock does a bit of both, with no friendly fire. Fire will damage them over time, and makes parasites unable to attack.

When on Hard or Insane difficulty, using your grenades and items becomes increasingly important, because of the larger groups. Aside from that, the main change in strategy is to simply not stay in one location for any longer then required, lest you run out of ammo.

Brutal is impossible. No, really. The original Alien Swarm developers couldn't do it. The real trick to finishing it is to use speedrun techniques, instead of playing normally.

Medics are the only ones that can cure infestation. Don't try to burn, punch, or shoot it off. You're just killing them. With Faith, you need to drop two Heal Beacons, and Bastille needs three. You'll need to heal roughly 200 HP.

Techs are most affected by a laggy game, since they interact with the environment the most. They weld doors, speed up sentry builds, and hack computers. The conveyer belt/1's hack is very prone to lag. Also, to skip the OS loading screen and go directly to the 1's game, press the Use key again.

Most weapons have five spare magazines, or ten – and they take 20% or 10% out of an Ammo Box. In other words, one full Ammo Box will fully resupply one weapon. Thus, bringing spare ammo in your loadout instead of a weapon will have the value of three additional weapons! If you don't need the versatility in another weapon, bring some ammo.

If you have trouble with friendly fire, try keeping an eye on your laser sight, instead of your cursor or character. You cursor is a bit hard to see when it becomes a red X, but your entire laser will become a dotted line.

Problems with fire? If you don't have a fire extinguisher, try to roll. If the burning area is small enough, you may be able to roll through it without being harmed.

This Steam Guide can be used under the Creative Commons BY-NC-SA 4.0 licence.

Please credit me as "Eiri Sanada". In addition, please include a link leading back to this Steam guide.

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