Gives Isaac a fat bird 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 the nearest 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, albeit slower, 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 (9 damage per second). The rock waves can destroy obstacles.
If damage is taken in a room with no enemies, the familiar will directly go to the flying phase without performing the jump attack.
Contact damage can be dealt to nearby enemies even when the familiar jumps off of Isaac's head.
While the familiar is sitting on Isaac's head, it can be affected by certain character appearances. For example, it will appear fully black if obtained by Tainted Judas.
BFFS!: Spawns 4 rock waves in an X pattern and doubles contact damage. Damage of the jump and the rock waves is unaffected.