Spawns a familiar that drops a Heart, coin, Bomb, or Key (or any of their variations) alternatingly every 5 or 6 rooms.
Notes[]
Familiars that follow behind Isaac have a certain priority in how close their position is to him over other familiars, with Mystery Sack having the lowest priority at 6th and thus being farther from Isaac than familiars of different priorities.
Can spawn troll bombs.
Synergies[]
BFFS!: The familiar drops pickups alternatingly every 4 or 5 rooms.
In-game Footage[]
Trivia[]
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.