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IsaacHD Xxx form2 Isaac Rebirth

Fistula (フィステューラ Fisutūra) (also known as "Meat Ball" from the artbook) is a boss found in Caves and Catacombs.


Fistula's appearance is extremely grotesque-looking, made of pieces of rotten flesh (with red fleshy skins from the inside) sewn together with thick stitches to form a large sphere. It sports with several hair strings, warts, and holes. In Edmund's artwork (and including the one from Rebirth), a few Chargers can be seen peeking out from the holes.

Total HP: 60 (Large) + 4x15(Medium) +8x8(Small) = 184


Fistula large

Larger form.

It resembles Envy in how it behaves, beginning as a single entity before splitting into four smaller entities upon taking damage, which then each split into two with further damage. However, unlike Envy, when reduced to the lowest size, the sections become Chargers.

Fistula medium

Medium-sized form.

The smaller a piece becomes, the faster it moves around. Pieces can also collide with each other, which changes their direction. Because of this, it is recommended to leave bigger parts intact for as long as possible, and focus on one part at a time. That way, the movement of the parts is more predictable, making the parts easier to dodge. It is also advised to kill the Charger before moving onto the next part, if possible. 

Despite floating in the air, Fistula and its parts cannot move over Rocks. However, as of the Wrath of the Lamb expansion, it can move over Pits.

Fistula small

Smaller form.

Fistula appears regularly as a Mini-Boss starting from The Caves to Sheol. In The Caves and The Depths, it starts as two smaller entities, and in The Womb and Sheol, a whole Fistula appears.

Champion Variants[]

Dark Blue[]

Fisula Dark

Total HP: 75 (Large) + 3x18.75 (Medium) + 6x10(Small) = 191.25

In this form, it will initially split into three entities instead of four and will spawn Boom Flies and Red Boom Flies on death. This version of Fistula has slightly more health, is larger, and moves slower.


Eternal Fistula

Every time it splits, it shoots 8-way bullets. It also spawns Eternal Spitties on death.


  • As a miniboss, Fistula will not spawn a Charger or Boom Fly if the smallest part is killed above a pit.


  • Page 24

    Fistula in the Artbook.

    From the artbook, Chargers seem to peek out of the holes while Fistula's smaller parts move around.
  • Fistula appeared in the demo from the original game.
  • The tradition of fighting the boss with its parts breaking into smaller and smaller pieces is based on the arcade classic Asteroids.
  • A fistula is a medical condition in which organs and other bodily tissues are abnormally connected to each other.
  • The name "Fistula" is used for another enemy in another game by Edmund McMillen: a flash game called The C-Word on Newgrounds.
  • It's also notable that in the background of Host, another one of Edmund's games, there is what appears to be a Fistula.
  • Fistula also slightly resembles a dead Dumpling, a creature from his Badlands series.
  • In older versions, Fistula used to shake while moving. Since the Wrath of the Lamb update, it no longer does so.


  • Using Mom's Bra on the first form can cause subsequent forms to get stuck behind rocks, making this boss unbeatable if the player cannot break the rocks. The same is true with Teratoma.
  • Using Mom's Pad on any form may cause it to become trapped in rocks making it impossible to defeat without destroying the rocks. The same is true about Teratoma.



Standard Bosses Dukeofflies fullThe Duke of FliesGemini fullGemini260x185-400px-Monstro.svgMonstroLarryjr fullLarry Jr.FistulaFistulaGurdy fullGurdyPeep FullPeepChubChubLoki fullLokiScolex fullScolexBlastocyst fullBlastocystTheFallen FullThe Fallen

Wrath of the Lamb DLC: 260x200-400px-Widow3WidowPin cleanPinMask of InfamyMask of InfamyGurdjrGurdy Jr.VS DaddyLonglegsDaddy Long Legs

Posthumous Bosses 285x230-MonstroII fullMonstro II

Wrath of the Lamb DLC: The HuskThe Husk260x220-The Hollow2The Hollow250x200-Teratoma.TeratomaLokii cutoutLokiiBlighted ovumBlighted OvumCarrionqueenThe Carrion QueenThe WretchedThe WretchedBc BloatThe Bloat

Alternate Bosses 287x265-Steven FullsizeStevenChub fullC.H.A.D.Gish fullGish

Wrath of the Lamb DLC: 200x300-400px-Triachnid boss portraitTriachnid

Harbingers 220x287-Isaac Vs famine edited- noobletkFamineBC PestilencePestilenceBC WarWarVSDeathDeath230x200-Headless HorsemanHeadless Horseman

Wrath of the Lamb DLC: BC ConquestConquest

Final Bosses 250x250-400px-MomMomMoms Heart FullMom's Heart250x250-ITLIVEScutoutIt LivesSatan FullSatan

Wrath of the Lamb DLC: Bc isaacIsaacBC xxx???