Spawns a hairball familiar that loosely follows behind Isaac, blocks shots, and can be swung like a flail to damage enemies.
The ball deals 5 damage per tick, but grows, increasing damage by 2 each time it kills an enemy — up to 5 times for a maximum of 13 damage. The damage it deals per tick (each half-second) is (level × 2) + 3.
The hairball level decreases upon entering a new floor: if level 2, it reverts to level 1. If level 3 or 4, it reverts to level 2. If level 5, it reverts to level 3.
This item belongs to the Guppy set. Collecting three items from this set will transform Isaac into Guppy.
The hairball's hitbox is the same size regardless of level.
If Isaac has transformed into Guppy, Guppy's Hair Ball spawns Blue Flies when it deals damage.