Blood Puppy

Effects

Spawns a familiar that chases nearby enemies and deals 2 contact damage to them per tick (4 per second).
After killing 15 enemies, Blood Puppy becomes angry, and changes in the following ways:
- Deals 7.5 damage per tick instead of 2 (15 per second).
- Charges at enemies that are aligned with it in the cardinal directions.
  - If Blood Puppy charges into a live bomb, it will get caught on its mouth, preventing it from moving until it explodes.
- Drops a half red heart for every 10 enemies it kills.
- Will also try to attack Isaac, dealing a half heart of contact damage to him.
- Can be damaged by Isaac, returning it to normal after it takes enough damage. Blood Puppy has 20 health and 90 Armor (effective health is ~140-180).
After getting 25 more kills (40 total), the angry version evolves, gaining the following modifications:
- Becomes much larger and deals 15 damage per tick instead of 7.5 (30 per second).
- Destroys obstacles it runs into while charging.
- Deals a full heart of damage to Isaac instead of half a heart.
- Drops a full red heart after every 10 kills instead of a half red heart.
- Has 50 health instead of 20 (effective health is ~400-500).

Blood Puppy appears in the bestiary as a type of monster, if the player turns it back to normal after it becomes angry. This is required to complete the bestiary.
Blood Puppy is not targeted by other familiars while it is angry.
- Blue Flies and other familiars that deal contact damage will still damage Blood Puppy if they happen to collide.
Since bombs ignore armor, a single bomb will tame the Blood Puppy.
Stages 2 and 3 of Blood Puppy are an enemy for all intents and purposes, similar to Dark Esau. This means it can be affected by, for example, the slow effect of Broken Watch.
Friendly Blood Puppies will spawn beside Isaac when he enters a new room while hostile ones will spawn in the middle or opposite ends of the room.
Starting the Dogma or Mega Satan fight while Blood Puppy is angry can be dangerous, as it will let Blood Puppy attack the player while the player is unable to move during the boss spawning animation.

(Ace of Spades) Ace of Spades / (Ace of Clubs) Ace of Clubs / (Ace of Diamonds) Ace of Diamonds / (Ace of Hearts) Ace of Hearts: Using them on an angry Blood Puppy will spawn the respective pickup and tame it.
BFFS!: Only increases the size and damage of Blood Puppy during its first phase.
Box of Friends: Tames an angry Blood Puppy and spawns another temporary one.
Camo Undies: While the camo effect is active, stages 2 and 3 of the Blood Puppy will not target Isaac, but will still target other enemies, making it safer for the player.
Eraser: Using Eraser on Blood Puppy while it's angry will permanently prevent it from advancing to the erased phase. Using it on phase two will prevent it from becoming angry altogether.
Friendly Ball: Using the ball on an angered Blood Puppy will instantly tame it. Using the ball again results in a purely cosmetic blood explosion.
Humbling Bundle will allow angry Blood Puppy to drop double red hearts.
GB Bug: Hitting Blood Puppy with GB Bug will transform it into a random enemy and spawn a tamed Blood Puppy.
Meat Cleaver: If Blood Puppy is angry, splits it into two copies. One copy can level up and be tamed like normal, but the other cannot level up and dies instead of being tamed.