Part 8

Learn how to defeat the Fistula boss in The Binding of Isaac: Rebirth. Understand its division mechanics and strategies for managing Chargers.

Fistula is a boss found in the Caves in The Binding of Isaac: Rebirth. This boss is similar to the Mini-Boss Envy, but its destructible parts are larger, have more health, divide differently, and spawn a Charger enemy upon destruction. The core strategy is to always destroy the smallest divisions on screen first. If multiple divisions are the same size, choose the easiest one. If a Charger appears, defeat it before destroying another part of Fistula. This method limits the number of on-screen objects to five, down from a potential maximum of eight.

Fistula begins as a single, large, floating entity that moves around the room, bouncing off obstacles and walls. After taking enough damage, it splits into four parts, which act as individual entities with the same AI but move faster. Each of these divisions, upon taking enough damage, splits in half again. These further divisions move even faster. When these final divisions are destroyed, they spawn a Charger that should be dealt with immediately.

While it may seem safer to stay in one spot, you must chase the chosen division to ensure its destruction. Try to move around the edges of the room, as this reduces the area you need to monitor from 360 degrees to 180 degrees. Projectiles can subtly affect the divisions' paths if they hit them, altering their direction slightly. Fistula is not a flying boss and cannot move over obstacles like rocks or pits.

This battle can become frantic, but by approaching it methodically and cautiously, you can ensure no more than five divisions are on screen at any given time.