Bird Cage

Effects

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) 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.
Sacrificial Altar: Can be used after the familiar has jumped.
Spin to Win: Boosts the familiar's damage while spinning, although has no effect on its speed.

Bird Cage: Multiple copies of the item provide no benefit and won't make more than one familiar appear.
Box of Friends: Immediately makes the familiar jump, leaving a ghost copy on Isaac's head until he takes damage. This has no benefit to the damage dealt and will not spawn more than one familiar.