The Stain

The Stain is a boss added in Afterbirth that can appear in all environments of Chapter 2, and is the posthumous version of Polycephalus.

Behavior

In a similar manner to Polycephalus, The Stain will go underground when Isaac is not within reach. While underground (and invisible), when The Stain and Isaac are closer together, it will pop out and unleash one of the following attacks:

Barrage of numerous bullets in all directions. The first barrage starts with fast-moving bullets that slow down. The second barrage starts with slow-moving bullets that speed up.
- This attack can be the most dangerous out of all his attacks, especially if there is more than one Stain on screen.
A horizontal melee tentacle attack from the left and right. This leaves Red Creep behind on each side of The Stain as well.
Spawns two Chargers and can have a maximum of two.

Champion Versions

Grey: Spawns Round Worms instead of Chargers and never fires barrages of bullets.

Gallery

The Stain ingame.
The Stain performing its bullet attack.
The Grey Champion Stain.
The Stain as one of Delirium's forms.

Arena

When fighting The Stain following obstacles can spawn:

Nothing
2 red poops (near upper-right and bottom-left corners)
2 red poops (near the center)
4 red poops (in all corners)
2x2 Pits in upper-right and bottom-left corners

Trivia

2 Stains will usually spawn for the nightmare wave for the 6th floor of Greed Mode.
A third head can be seen in the background in The Stain's boss art.
During the versus screen, The Stain's popping out sound can be heard. The Stain is one of six bosses that can be heard in the versus screen; the other five are The Forsaken, Big Horn, Mom, Mom's Heart and It Lives.
Prior to Booster Pack #5, The Stain could spawn Drowned Chargers if it was fought in the Flooded Caves. This also applies to Chub.