A Regular Mook is the standard opponent. Toting an assault rifle, he'll lay down fire when he detects a bro until one of them dies. He can be parachuted and can spawn from a Mook Door. Despite their low rate of fire, they are one of the more common source of deaths for anyone who does not pay attention to the "!" symbol, and their false sense of security. They are weak individually but extremely terrifying when in a horde. For Example, a Mook Truck.
The Suicide Mook will search for bros, charge them and detonate. This can be a game changer in tight quarters. You're best to knock these mooks back from a distance. They will detonate shortly after they are dead. He can be parachuted and can spawn from a Mook Door.
A Riot Shield Mook hides behind his riot shield that can withstand sustained primary attacks as well as deflecting certain projectiles. But any melee attack/fire/explosion will knock off the shield, leaving him completely defenseless.
A Bruiser can take more damage. He uses a minigun, which spins up, shoots a spray of bullets, then stops for a few seconds.
A Scout Mook looks for players and after detecting one, runs around alerting other hostile units of their presence. Any unit he passes will be alerted to the player's presence unntil killed. They will also trigger any nearby alarms,
An attack dog is a close range opponent that moves quickly and jumps onto nearby bros. Its attack kills instantly. If it finds a corpse, it will feed on it and become a bigger and stronger version, called Super-Size-Me Dog. This bigger dog can take more damage.
A Super Mook is completely impervious to all attacks and shoots very dangerous flurries of bullets. His only weakness is a fall of three or more blocks/jacking. Bros can jump on him. After his death, bros can ride in its armor (Entered using the melee button): his fuel will deplete from flying by the jetpack, (something the mook never does). Fuel can be replenished with ammo crates. The mech can also be self-destructed using the special attack button to do moderate damage to the terrain and surrounding mooks. Being hit simultaneously by two Armored Mooks' fire will cause the player to jump out and likely die. In the full release, you can eject the mook out of the suit (by pressing melee when you're standing on it) and take it over outright.
A Grenadier Mook will toss grenades in a bro's direction, and also drop one when they die. Each time one of their corpses is hit, a grenade is dropped from it. His grenades can be thrown back by pressing the melee attack near them.
A Bazooka Mook will launch destroyable homing rockets to bros, making them very dangerous unless shielded by terrain. However due to their rockets caused friendly fire, they can kill other enemies.
A Ninja Mook is an opponent who is lying on the ground until a bro gets close enough, then they jump out and attack. It can be hidden by a Foreground Bush Doodad. They are statistically the same as a Regular Mook and are usually given away by the curiosity sign of "?".
A Jetpack Mook is an opponent who hovers above when seeing a player. Upon death its corpse acts like a Propane Tank going to the direction he's facing before exploding.
A Xenomorph with a device on its head. They are like normal Xenomorphs, except that due to the box that controls their minds, they are friendly to terrorists and hostile to players and other aliens without brainbox. They also splash acidic blood after being killed. They are afraid of other normal aliens. They are currently not present in campaign (Full Release). However they can be used in level editors.
An Alien Egg spawns a Facehugger if it is touched or stepped on. Eggs can be destroyed before they hatch. They can be found on floors, walls, and ceilings.
Oval-shaped cocoons that release lethal acid drops when a Bro pass under them. If destroyed, they explode in a huge acidic blast. They are also screecher eggs.
A Facehugger is a small, crawling form of the alien. It crawls on floors, ceilings, and walls, seeking a bro or mook. When the facehugger finds one, it latches onto the face and kills the bro or mook. After a few moments, a Xenomorph hatches from the host body. To prevent this, a bro must destroy the body before the alien hatches. There are many accidental ways to get rid of Facehuggers.
A stout beetle-like alien which can roll up into a fast ball and detonates when a Bro is near or runs out of time, spraying acid everywhere.
It is an aerial variant of the Screecher, being physically identical aside from its wings, rather than rolling, however, banelings dive-bomb onto their enemies before exploding.
An enormous trap similar to a needle, these things hide in infested terrain and shoot up to impale nearby Bros/Enemies. However sprinting completely negates this issue, and if a Xenomorph is impaled, their acidic blood will often destroy the Spine.
An Xenomorph is a large, quadrupedal alien that hunts for bros and mooks. They move quickly and spawn from unseen parts of the map. When a xenomorph is killed, it splashes acidic blood. This blood deals no harm to players, but it does dissolve parts of the terrain if possible.
Larger Xenomorphs the size of an elephant that charge towards the player when alerted and have a much higher health count compared to regular Xenomorphs. Their corpses can never be destroyed unless fall out of bounds.
Like the Terrorkrawler and Acid Crawler, the Broodworm only appers at certain points in the game. It's a brown-green worm that vomits Facehuggers and chomps the player if they are close enough. They are rather easy to counter.
Regular Mooks possessed by an evil spirit; giving them a green pallor and burning away their shirts. They revive continuously unless gibbed, decapitated, desecrated, impaled by spikes or attacked with a weapon that uses a silenced weapon kill animation like Brade's throwing knives or Snake's Dual Uzis.
Mooks swollen like living bombs by an evil spirit, they self destruct in a powerful bloody explosion to kill a player. Spawned engorged mooks by Warlocks/Satan are usually immobile since their arm and legs are too short to reach the ground and thus cannot move on it's own, what makes them dangerous are those demonic spells that toss them around once for each. Others that are pre-placed on the map are mobile and can use their legs. Upon reaching the ledge, they tend to make a small jump, which makes them more dangerous than Regular Suicide Bombers that only idiotically runs.
Sorcerers who wear dark hooded robes, they quickly summon Engorged Mooks and toss them like grenades if they see a Bro and has nearly unlimited range-There's nowhere they can't go, but it's everywhere the unexpected shows up. Destroy the Warlocks to stop this rampage or just run VERY far away. Warlocks usually are located very high up to prevent themselves killed easily.
Weak but dangerous foes, these disembodied skulls dive bomb like Homing Rockets when they spot a Bro. But they became a little less dangerous when the player is using a long-range knock-back weapon, due to having low health they can be easily defeated and while this will not instantly destroy them, it knocks them back to enemies, causing more chaos.
Warped canine monsters with a gaping maw instead of a snout, they rapidly spawn clones of themselves instead of getting stronger after eating a corpse. If left alone, they can generate a very large army, but are quickly defeated by rapid fire.
Similar to the victims of Brodator's melee attack, these enemies pursue the Bros and latch to them at contact. They don't make any harm but hinder some movements, and can even take a hit for a Bro that would otherwise kill them. They can be thrown away by holding the melee button. The Skinless Mook will hide in pools of blood inside of Hell. They are quite hard to see due to their red colouration and crouching pose, but are given away by the "?" that appears when a Bro is nearby, like how Ninja Mooks are given away.
An enormous reanimated corpse, missing its arms, eyes, and ears, as well having high health. It vomits a volley of acid upon detecting a player, violently exploding and splitting into engorged mooks upon death.
A variant of Boomer, having a paler color and a sewn mouth. Upon spotting a player, they self-destruct and creates a cluster of five Lost Souls.
Being the reanimated corpses of Bruisers, they are quite a bit stronger than their normal counterpart. Their miniguns having been replaced by multi barreled flamethrowers, their attacks are similar to Ellen's special, but deals no damage to terrain and gibs upon contact. Unlike their smaller kin, they do not reanimate after death, due to being significantly harder to defeat.
Men and women hurt by the Mook Army, they can fight for the Bros if given a weapon (melee button). But it's best not to waste your time rescuing them as they are pretty idiotic and don't use their weapons properly. They also take fall damage, cannot climb walls, and usually walks inside minefields/traps/bottomless pits. However, they can take a shot or two for the player.
Strange bald humanoids tortured by the Demons, they can help the Bros like Villagers. When killed, their mouth is left agape with their tongue dangling.
Bees are released by destroying a beehive. They attack any enemy in their reach.
Animals that will explode in a burst of bacon slices if killed with an explosive. If you current bro's melee attack is a knife, you can fly by spam-clicking melee while standing on top of its corpse. (AKA The Incredible Flying Pig Glitch)
White birds common in the sky and forests.
Dark birds found where Demons thrive.
A mutated earthworm found near alien Hives, it creates a puddle of green goo if squashed.
Revolting gray worms that swarm in Demon territory and come out the neck stumps of decapitated Undead Mooks/Destroyed Boomers. They produce blood when a player squashes them.