A Regular Mook is the standard opponent and the most common. Toting an assault rifle, he'll lay down fire when he detects a bro until one of them dies. He can be parachuted and 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.
To destroy a mook door, destroy all below terrain nearby, it will create a violent explosion so stay clear.
The Suicide Mook will search for bros, charge them and detonate. This can be a game changer in tight quarters. It's best to knock these mooks back from a distance so as not to get caught in the explosion. They will detonate shortly after they are dead. He can be parachuted and spawn from a Mook Door. His explosions is a double edged sword so if he's knocked into a bunch of mooks then it can benefit.
They can also be the destruction of a mook door as enemys will continute to fall out of it until the door collapses in of it self and can't be exited from anymore
A Riot Shield Mook hides behind his riot shield, it will be thrown off after sustaining some prolonged fire or instantly with the melee command . He can be very help full to stop bullets from hitting other Mooks alike. However splash damage cannot be blocked and ricocheted bullets may hit other mooks.
If he is not killed and the shield is thrown off, he will be unable to retaliate due to being unarmed.
Throwing him will remove the shield
A Bruiser can take more damage and spool up a minigun. They are very dangerous and can be tricky to combat. MacBrover's special can be used to effectively lure him and will destroy him if close, or using his fire command can plant a bomb onto him/nearby him can be also effective.
A Scout Mook looks for bros and after detecting one, runs around alerting other hostile units of their presence. And will also use nearby alarms that can potentially summon endless amounts of mooks, it's best to kill them quickly. They also have no depth perception and can often run off high buildings and die.
Scoust will also not detect corpses blood or anything that's normally incriminating like other mooks
An attack dog is a close range opponent that will jump into nearby bros. It will feed on a corpse when it finds one until its destruction and will then howl before becoming a bigger and stronger version called Super-Size-Me Dog which is, obviously, tougher than a normal dog. The attack dog is drawn to the sound of gunfire, and will automatically detect a bro if it hears a shot. They are extremely deadly and agile, yet can be killed easily if the player was alert.
An Armored Mook will resist to a tremendous amount of bullet damage and will shoot very dangerous flurries of bullets like the Big Mook, but he is weak to falls. Bros can jump on him. After his death(or, simply press the melee button to hijack which kills the mook inside), bros can ride in its armor (Entered using the melee button): his fuel will deplete from flying (something the mook never does). Fuel can be replenished with ammo crates. The Armored Mook can also be self-destructed (using the special attack button) to do moderate damage to the terrain and surrounding mooks. Will explode when it has taken too much damage from falling and explosions. Being hit simultaneously by two Armored Mooks' fire will cause your bro to jump out (and likely die).
You can get a same suit after completing a covert operation, particularly the one with many of these Armored Mooks. After completion you will unlock the Mech Drop which can be opened from crates with a skull icon on them (Pretty rare though). If using the special will place down a flare, a Mech will drop to the location soon so get on and fight. Useful during some Hell stages. The only difference is, the ones you ride from the Mooks has a skull icon while the ones you obtain from mech drops will have a USA flag on them instead.
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 rockets to bros. Their rockets are homing, making them very dangerous. They can blow up other mooks too.
A Ninja Mook is an opponent who lays down until a bro gets close enough. It can be hidden by a Foreground Bush Doodad Or Alien Fronds but a tiny bit of the Ninja Mook but a pixel can still be seen. They will behave like a basic mook once leaped out.
A Jetpack Mook is an opponent who hover if seeing a bro. Upon death his jetpack acts as a Propane Tank going to the direction he's facing before exploding. They have the same fire rate as a Mook.