Grab Bag
The Grab Bag will spawn 1-4 random pickups upon touching it. They will not drop any hearts, pills, or chests, and they have an increased chance to drop Lil' Batteries. Sack Head has a 33% chance to replace pickups with sacks. Shops have a chance to sell sacks for seven coins.
Random sacks have a 99.0% chance to be a grab bag.
Black Sack
A Black Sack will spawn 2-3 pills, Black Hearts or Bone Hearts, and/or Bombs when collected. Only one heart can spawn from one sack, but there may be two pills or bombs.
Random sacks have a 1% chance to be a black sack.
Sacks will replace Black Sacks until unlocked.
Notes
- Bone hearts can spawn from Black Sacks even if they haven't been unlocked yet.
- The probabilities above refer to the kind of sack that is generated by the game when a sack is spawned with a sub-type of 0 (i.e. a random sack).