Spawns a familiar that follows Isaac and drops a Grab Bag once every few rooms cleared.
The rate alternates between every 5 or 6 rooms.
The rate alternates between every 7 or 8 rooms.
Notes
Familiars that follow behind Isaac have a certain priority in how close their position is to him over other familiars, with Sack of Sacks having the lowest priority at 6th / 8th and thus being farther from Isaac than familiars of different priorities.
Synergies
BFFS!: The drop rate is improved to every 4-5 rooms.
Grab Bag once every few rooms cleared.
The rate alternates between every 5 or 6 rooms.
The rate alternates between every 7 or 8 rooms.
6th / 
8th and thus being farther from Isaac than familiars of different priorities.
BFFS!: The drop rate is improved to every 4-5 rooms.
Sack of Pennies, 
Rune Bag, 
Mystery Sack, and 
Bomb Bag.
Cain Unlocks 
Ultra Greedier Unlocks 
The Binding of Isaac: Rebirth
