Mulligan

Mulligans are enemies with tear-filled eyes and a bloated head that appear in Chapter 1. Mulligans are afraid of Isaac and will actively try to avoid him; their eyes widen and their speed increases when doing so. In their panicked state, they may stumble over spikes or into a fire.

Upon death, they can spawn several Flies, Attack Flies and, occasionally, a Pooter. Mulligans may self-detonate, indicated by them holding their breath and inflating; in addition to spawning flies as normal, it will also fire four shots in the cardinal directions and destroy nearby objects when doing so. Mulligans cannot deal contact damage to Isaac ( unless they are Champions).

In later chapters, deformed variants of Mulligans will appear.

Mulligoon
Mulligoons display a depressed appearance, but unlike Mulligans, they do not have tears in their eyes. Their skin is a darker shade and one eye appears to be missing. Much like Mulligans, they are afraid of Isaac and will run away from him, don’t deal contact damage, and can self-detonate. They release 4 projectiles in all diagonal directions and drop a Troll bomb on death. If they self-detonate, they release 8 projectiles in all directions rather than 4 in the ordinal directions in addition to dropping a Troll bomb.

Mulliboom
Mullibooms have a bomb wedged into their head. Instead of avoiding Isaac like all other Mulligan-types, they will charge at him and explode on contact, dealing half a heart of damage. They also explode immediately if they are killed, similar to Boom Flies. Make sure to keep a safe distance when delivering the final shot, and consider killing them next to a tinted rock or a wall that might be adjacent to a Secret Room.

Hive
Hives are Mulligan variants with a rotting head and no eyes. They can be found in Chapter 2 and Chapter 3. They behave similarly to Mulligans, including evading Isaac and spawning flies upon death. However, they also occasionally spit Attack Flies while running away from Isaac, and unlike Mulligans and Mulligoons, they can't self-detonate. Hives have higher health than Mulligans.

Drowned Hive
Drowned Hives behave similarly to Hives but spit Drowned Chargers instead of Attack Flies. Upon death, they spawn 1-2 Drowned Chargers. Drowned Chargers spawned by Drowned Hives have half their usual health (11 HP).

Nest
Nests are a new enemy variant in Rebirth. They are Mulligan variants that behave similarly to Hives, but they spit Spiders instead of Attack Flies. They spawn a Trite or a Big Spider upon death. Nests share the same high health as Hives.

Leper
Lepers are a Mulligan variant introduced in Booster Pack #5. Lepers alternate between walking towards and running away from Isaac. For every 15 damage they take, a chunk of their head, known as a Leper Flesh, will detach and start erratically chasing Isaac. Lepers deal contact damage if they are in this state or below. Lepers can naturally be found with some head chunks missing.

After being reduced to 15 health, Lepers will chase Isaac continuously, leaving a trail of damaging Red Creep. Upon death, they leave behind one Leper Flesh and a Grey-colored Gusher.

Leper Flesh
Leper Fleshes are head chunks from Lepers that erratically chase Isaac and are spawned from Lepers for every 15 damage they take. Upon death, they fire a red blood shot at Isaac.

They will die if Isaac walks into them, though this will result in Isaac taking damage.

Holy Mulligan
Holy Mulligans are a Mulligan variant introduced in The Binding of Isaac: Repentance. In contrast to all variants, this one smiles, yet in comparison, it still makes the same sound effects and continues to avoid Isaac. They spawn a Small Angelic Baby as their means of attack when Isaac gets close. When killed, they leave behind 1-2 Embryos.

Prey
Preys are a Mulligan variant introduced in The Binding of Isaac: Repentance that appear in the and  as different versions. They spawn Small Leeches. Upon death, they also spawn 2-3 of Small Leeches.

Mullighoul
Mullighouls are a Mulligan variant introduced in The Binding of Isaac: Repentance. They can occasionally spawn a Willo, and will spawn 1-2 upon death. Despite their ghostly appearance, they cannot fly over obstacles nor gaps.

Fartigan
Fartigans act similar to Mullibooms, except that they hock up explosive gas as they chase Isaac. Upon death, they release an explosive shot that also blows up any gas clouds it hits.

Bouncer
Bouncers behave like regular Mulligans; however, after some time or when they're close to death, their head inflates and they start chasing Isaac. If they die or touch him in this state, they explode into a spectacle of blood shots with some lingering in the air before dropping down. If they are killed before they enter this hostile form, they release 4 blood shots in all diagonal directions.

They can also reflect shots in their inflated state.

Tainted Mulligan
Tainted Mulligans are much tankier and stronger versions of Mulligans. They walk away from Isaac and will spit several Ring Flies at him if he is near. Upon death, they spawn a plethora of fly enemies — Flies, Suckers, Spits, Inks, Boom Flies, and Red Boom Flies.

It should be noted that they can be killed instantly with a bomb, regardless of damage or bomb modifiers.

They are exclusive to the Ascent to.

Trivia

 * The Mulligan, Mulligoon, Hive, and Swarmer are all the same monster in stages of decay and infestation.
 * In the original Binding of Isaac, when a Mulligan self-detonated, the explosion would not break rocks.
 * Mulligans will start running in random directions instead of directly away from Isaac if he stays close to them for long enough. This behavior also applies to Small Baby Long Legs.
 * Mulligans, Mulligoons, and Mullibooms can be manipulated into destroying tinted rocks and opening Secret Room doors. Mulligoons and Mullibooms only need to be positioned next to the item before being killed, while Mulligans have to be pushed into a corner where the item is and baited into self-detonating. Example
 * In the game's files, there is an unused Mulliboom self-detonation animation, an unused graphic of a Hive with a Mulligoon's face, and an unused graphic of the Drowned Hive with a blue-tinted Mulligoon's face.
 * Drowned Hives, along with Drowned Chargers (name of Drowned Charger wasn't revealed), were revealed for Afterbirth in this official Binding of Isaac post.
 * A leper is a person who suffers from leprosy, which is a contagious disease that causes discoloration and lumping on the skin plus disfigurement and deformities.
 * Due to the Holy Mulligan leaving behind Embryos on death, it could be suggested that it transforms Embryos into the Small Angelic Babies it spawns.
 * Holy Mulligans, Holy Bonies, and Holy Eyes originated as cards from the card game The Binding of Isaac: Four Souls.