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.
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. Note that a Charger will not spawn if the smallest part is killed above a Pit.
In this form, it will initially split into three entities instead of four and will spawn Boom Flies on death. This version of Fistula has slightly more health, is larger, and moves slower.
- 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.
- Fistula appeared in the demo.
- It is also simply referred to as the "Meat Ball" in the Unholy Edition art booklet.
- 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: a flash game called "The C-Word" on Newgrounds.
- It is also notable that 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 Edmund's old series "The Badlands"
- In older versions, Fistula used to shake while moving. Since the Wrath of the Lamb update, it no longer does so.
|Basement||Larry Jr. • Monstro • The Duke of Flies • Gemini • Steven • Famine|
|Cellar||Widow • Pin • The Duke of Flies • Famine • Gurdy Jr. • The Blighted Ovum|
|The Caves||Fistula • Peep • Gurdy • Chub • C.H.A.D. • Pestilence|
|Catacombs||The Husk • The Hollow • The Blighted Ovum • The Carrion Queen • Peep • Pestilence • The Wretched • Gurdy Jr.|
|The Depths||Loki • Monstro II • Gish • War • Mom|
|Necropolis||Mask of Infamy • Daddy Long Legs • The Carrion Queen • The Bloat • Loki • War • The Wretched • Mom|
|The Womb||Scolex • Blastocyst • The Bloat • Death • Conquest • Daddy Long Legs • Triachnid • Teratoma • Mom's Heart • It Lives|
|Utero||Teratoma • The Bloat • Death • Conquest • Daddy Long Legs • Triachnid • Lokii • Mom's Heart • It Lives|
|Sheol||The Fallen • Satan|
|First to fifth and seventh level||The Fallen • Headless Horseman|