From Binding of Isaac: Rebirth Wiki
Jump to: navigation, search
Boss Blastocyst.png
Base HP
Large: 190
Medium: 75
Small: 30
Embryo: 12
Stage HP
Found In
Stage womb.pngStage utero.png
Dropped Items
Boss Boss  

Blastocyst is a boss that spawns in The Womb / Utero. It is a large blob with a small Embryo inside.

Behavior[edit | edit source]

  • Hops around the room randomly and shoots tears in all directions.
  • Once enough health is depleted, it will split into two medium versions of itself, which shoots 6 tears in all directions.
  • These two medium blastocysts each split into two smaller forms, which shoot smaller tears in 4 directions.
  • When all the parts of the blastocyst are defeated, they will become a bouncing Embryo that does contact damage.

Blastocyst is perhaps the least complicated boss in this chapter, having essentially one attack that gets weaker for each split. Any sort of piercing tears or items such as Technology 2 or Brimstone can defeat this boss extremely quickly.

Gallery[edit | edit source]

Trivia[edit | edit source]

  • 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 second level 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.
  • 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 a blastocyst, it seems as though, for a split second, an audio clip of someone's voice can be heard. To better hear it, listen with headphones without the music.
  • Afterbirth† Indicator.png Prior to an update, an unfair room existed in The Womb consisting of 8 Blastocysts as result of unintentionally placing full sized ones rather than small ones.

Bosses Boss Monstro.png
Chapter 1 Blighted OvumDingleThe Duke of FliesFamineFistulaGeminiGurdy Jr.GurglingsThe HauntLarry Jr.MonstroPinStevenWidow
DLC Indicator.png DangleLittle HornRag ManTurdlings
Chapter 2 C.H.A.D.ChubDark OneGurdyGurdy Jr.The HollowThe HuskMega FattyMega MawPeepPestilencePolycephalusCarrion QueenThe Wretched
DLC Indicator.png The ForsakenThe FrailThe Stain
Afterbirth† Indicator.png Big HornRag Mega
Chapter 3 The AdversaryThe BloatThe CageCarrion QueenThe GateGishLokiMask of InfamyMonstro IIWarThe WretchedMom
DLC Indicator.png Brownie
Afterbirth† Indicator.png Sisters Vis
Chapter 4 BlastocystThe BloatConquestDaddy Long LegsDeathIt LivesLokiiMama GurdyMom's HeartMr. FredScolexTeratomaTriachnid
DLC Indicator.png Blue Womb DLC Indicator.png Hush
Chapter 5 The FallenIsaacSatan
Chapter 6 ???The LambMega Satan
DLC Indicator.png Greed Mode DLC Indicator.png Ultra Greed
Afterbirth† Indicator.png Ultra Greedier
Afterbirth† Indicator.png The Void Afterbirth† Indicator.png Delirium
Chapters 1-4 The FallenThe Headless Horseman

SmallIsaac.png The Binding of Isaac: Rebirth SmallIsaac.png

MainPageAchievements.png Achievements MainPageAttributes.png Attributes MainPageBosses.png Bosses TarotCard.png Cards and Runes MainPageChallenges.png Challenges MainPageChapters.png Chapters
Isaac App.png Characters MainPageBabies.png Co-op Magic Mushroom Icon.png Items Isaac's Tears Icon.png Item Pools MainPageMonsters.png Monsters MainPageObjects.png Objects
Red heart.png Pickups BlueBlue.png Pills MainPageRooms.png Rooms MainPageSeeds2.png Seeds Guppy App.png Transformations The Left Hand Icon.png Trinkets