Monsters

Monsters refers to the many antagonistic creatures the player will encounter throughout the game.

Most monsters (with few exceptions) will damage Isaac by either touching him or shooting him with projectiles. Less frequently, monsters will spawn additional, lesser monsters, spread creep, or attempt to affect the player's movement. Along with the more common variety of monsters, champion versions can be found lurking about. These monsters are often like their common counterparts, but have a color tint or size change and drop basic pickups on death. There are also champion versions of most bosses.

There are 196 naturally spawning monsters in total. 40 of them were added in Afterbirth and 21 were added in Afterbirth † (13 were added in Booster Packs). Almost all of these naturally spawning entities are featured in the Bestiary, with the exceptions being the Rag Man's Ragling and Suction Pitfall.

Champions

Some monsters can spawn as a Champion which deviates in coloration and size from its more common form. The champion's coloration denotes which peculiar behaviors and traits it will exhibit. Champions will generally drop a pickup (coinciding with the color of the champion) when killed on normal difficulty. However, in hard mode, the drop rate is reduced to 33%.

Most champions inflict full heart damage regardless of chapter and have double the health of a normal monster. Champions are generally regarded as more dangerous than common monsters.

Champions always deal contact damage, regardless of what monster they are (e.g. a common Mulligan will not deal contact damage, but champion versions will).

The identifying scheme for champion qualities is as follows:

ID	Appearance	Effect	Drop
0	Red	×2.5 amount of HP.	Heart
1	Yellow	Increased movement speed.	Little battery
2	Green	Leaves green creep as it walks.	Pill
3	Orange	Attacks cause you to drop coins (like Greed or a Hanger).	Coin
4	Blue	Decreased speed.	3 blue flies
5	Dark Green	Explodes when killed.	Bomb
6	Solid White	Invincible until all other enemies are killed.	Eternal Heart
7	Gray	2/3 health, decreased speed.	Key
8	Transparent White	Tears become spectral tears, and it can move past environmental obstacles (such as pits) that it otherwise couldn't when forced.	Golden Chest
9	Black	Fades in and out of visibility, like a Null.	Red Chest
10	Pink	Periodically shoots short-ranged blood shots, similar to Gushers.	Nothing
11	Purple	Pulls Isaac and his shots towards itself, like a Gaping Maw.	Random Trinket
12	Dark Red	Collapses into a flesh pile upon death and regenerates if not finished off (like a Globin).	1+1 Free Heart
13	Cyan	Releases blood shots in 8 directions when killed.	1/2 heart
14	Camouflage	The enemy blends into the background and briefly becomes visible when damaged.	Rune
15	Pulsing Green	Splits into two copies of itself upon death.	2 normal versions of itself
16	Pulsing Gray	Repels Isaac's shots when it pulses.	Nothing
17	Light White	Has 1-2 eternal flies circling it. Spawns another fly upon death.	Attack Fly
18	Small	Decreased health, increased speed and pitch of sound effects. Smaller and more difficult to hit.	One Makes You Small pill at 1/5th of difficulty based drop rate; can change other pills in the current rotation.
19	Large	Increased health, slightly decreased speed and decreased pitch of sound effects. Larger and easier to hit. Deals two full hearts of damage.	One Makes You Larger pill at 1/5th of difficulty based drop rate; can change other pills in the current rotation.
20	Pulsing Red	All other enemies in the room regenerate health rapidly while this enemy is alive. The regeneration heals about 20% of the enemies’s health once or twice per second.	Heart
21	Pulsating	Spawns an Attack Fly on hit. After each hit, there is a delay until the next hit results in another Attack Fly. A single Pulsating enemy can have up to 5 Attack Flies at once.	4-6 blue flies
22	Crown	Increased health. All enemies in the room that are not champions will turn yellow while the crowned enemy is alive. The affected enemies will drop batteries like yellow champions upon dying, but otherwise have no extra health, speed or damage.	2-3 random pickups
23	Skull	Produces a Necronomicon effect upon death. Deals two full hearts of damage.	Necronomicon effect

The chances for Champion monsters to appear are noted in the table below:

Modifiers	Normal mode	Hard mode	The Void
Base chance	5%	20%	75%
Champion Belt	20%	35%	75%
Purple Heart	10%	40%	100%
Purple Heart + Mom's Box	20%	80%	100%
Champion Belt + Purple Heart	40%	70%	100%
Champion Belt + Purple Heart + Mom's Box	80%	100%	100%

• Champion Belt adds 15% to the base champion chance. This has no effect in The Void.
• Purple Heart doubles the champion chance, and affects Champion's Belt.
• Mom's Box changes Purple Heart to quadruple the chances instead of doubling.

• 

  Concept art for the champion versions of the Nest.

Monster Replacements

Some monsters have a chance to be replaced with other monsters when they spawn, but only at room entry. Some replacements only occur on certain floors.

(Disclaimer: Chances are approximate!)

Base Monster	Replacement	Chance	Notes
Rebirth
		10%
		1%
		6%
		6%
		5%
		5%
		5%
		1%
		10%
		1%
		10%
		6%
		1%
		10%
		10%
		5%
		1%
		6%
		10%
		6%
		6%
		1%
		6%
		1%
		6%
		6%
Afterbirth
		60%	Exclusive to Burning Basement
		60%	Exclusive to Burning Basement Only a single Burning Basement room contains a Pale Fatty, making it a very unusual replacement to witness.
		60%	Exclusive to Burning Basement
		50%	Exclusive to Flooded Caves
		50%	Exclusive to Flooded Caves
		50%	Exclusive to Flooded Caves
		50%	Exclusive to Dank Depths
		50%	Exclusive to Dank Depths
		50%	Exclusive to Dank Depths
		50%	Exclusive to Scarred Womb
		50%	Exclusive to Scarred Womb
		50%	Exclusive to Scarred Womb
Afterbirth+
		10%
		20%
		20%
		20%
		20%
		20%
		10%
		20%
		20%
		40%	Exclusive to Burning Basement Rottys do not appear in any Burning Basement room layouts, but can still be replaced regardless.
		50%	Exclusive to Flooded Caves Dank Chargers do not appear in any Flooded Caves room layouts, but can still be replaced regardless.
		20%	Exclusive to Aprils Fool challenge

The Binding of Isaac: Rebirth
Achievements Challenges Completion Marks Items Trinkets Characters Chapters Rooms Transformations Attributes Bosses Monsters Pickups Modes Curses Objects Seeds Effects Endings
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