The first time Isaac takes damage in a room, a familiar leaps on an enemy, dealing damage and releasing a rock wave. For the rest of the room, it chases enemies similar to Dead Bird.
Quote
"Fat buddy"
Effects
Gives Isaac a familiar that sits on Isaac's head until he takes damage.
Upon taking damage, it will jump off of Isaac's head and land on a nearby enemy, dealing damage and creating a rock line in a random direction. For the rest of the room, it acts like Dead Bird, flying around and dealing contact damage to enemies.
Bird Cage does 45 damage to enemies it lands on and 10 damage per rock wave that hits enemies, then does 3 contact damage per tick while chasing enemies (6 damage per second). The rock waves can destroy obstacles.