Blastocyst

Base HP	Stage HP
190	0

Ingame Appearance

Entity ID
74.0

Found In
Boss








Degraded Boss
Small




Medium


Large

Dropped Items
Boss

Blastocyst is a boss that can appear:

• In all environments of Chapter 4 ( The Womb, Utero, Scarred Womb).
• Only in The Womb and Scarred Womb.

The large Blastocyst has 190 HP, the medium forms have 75 HP, and the small forms have 30 HP.

Behavior

Makes medium hops towards Isaac and can perform the following attacks:

• Hops in place and upon landing:
  • Shoots 8 projectiles in all directions.
  • Sends out a burst of large disorganized projectiles in all directions.
• Leaps off-screen and lands on Isaac's position; upon landing:
  • Shoots 12 small projectiles in all directions.
  • Shoots 8 larger projectiles in all directions.
• Once enough health is depleted, it will split into two medium versions of itself.
  • Each medium form can shoot 6 projectiles in all directions.
• Once enough health is depleted, each medium Blastocyst splits into two small versions.
  • Each small form can shoot 4 projectiles in the cardinal directions.
• Each of these small Blastocysts leaves an Embryo behind upon defeat.

Gallery

• 

  Blastocyst's appearance.

• 

  Medium Blastocyst's appearance.

• 

  Small Blastocyst's appearance.

• 

  Blastocyst as one of Delirium's forms.

Notes

• Blastocyst can be encountered in groups consisting of:
  • 1 large Blastocyst and 2 small Blastocysts.
  • 1 large Blastocyst and 6 Embryos.
  • 2 medium Blastocysts and 2 small Blastocysts.

Trivia

• Blastocyst appeared in the original The Binding of Isaac.
• An embryo is called a blastocyst when the differentiation of cells within a morula finally begins, usually 4–5 days after the fertilization of an embryo.
• It is very common for the medium form of the boss to spawn as normal enemies in rooms. On even later floors like Sheol, the full boss can even spawn as a common enemy.
• As Blastocyst divides, its positive facial expressions will become less happy, losing its smile entirely when it becomes an embryo.
• If Blastocyst is killed on spikes, none of the smaller versions will spawn. This can also apply if a very large amount of damage is dealt very quickly to any of the phases.
  • This can also happen if Blastocyst is killed while still having a debuff that actively harms it (e.g. poison, fire).
• Upon killing Blastocyst, it seems as though, for a split second, an audio clip of someone's voice can be heard. Which can be easier to make out with music turned off.
• During the DLC's release, an unfair room consisting of 8 Blastocysts with a Portal in the middle existed in all environments of Chapter 4 as a result of unintentionally placed full-sized ones rather than small ones. It was acknowledged by Edmund McMillen on Twitter and was fixed shortly after.
• Blastocyst's intro animation from the original game has been restored and it has new animations for when it divides.