Mystery Sack is an unlockable passive item.
- Spawns a familiar that drops a Heart, coin, bomb, or key (or any of their variations) alternatingly every 5 or 6 rooms.
- BFFS!: The familiar drops pickups alternatingly every 4 or 5 rooms.
- Before patch 1.04, this item did not drop any items or do anything at all. Why it did not work remains a mystery.
- This item is the only "bag" item (Sack of Pennies, Rune Bag, Bomb Bag, and Sack of Sacks), that isn't a counterpart to other existing bag items, rather being a combination of some.
PC A3ES 1TQN (First floor, Treasure room next to spawn)
PC QHKQ ZE4N (First floor, Treasure room next to spawn)
PS4 CGVC XKY3 (Play as Isaac, and reroll the first item in the secret room just below the starting room)
Vita Q73A BMMP (adjacent to starting room)
|The Lamb Unlocks|
|The Binding of Isaac: Rebirth|
|Achievements||Attributes||Bosses||Cards and Runes||Challenges||Chapters|