unlocked by beating the Cantripped! challenge. the challenge is unlocked alongside
You play as Tainted Cain, but instead of his usual crafting bag, he gets a different bag that holds passive and active items. It starts with 3 slots and after each boss you get a Starter Deck that adds another slot. Press Ctrl to cycle through items, and press Q to use it. You will only gain the item's effect for the current room, and active items are activated immediately upon pressing Q. You stock up on more items by picking up cards that drop from enemies and from clearing rooms, no item pedestals will appear besides the Starter Deck after bosses, and any item that would spawn a pedestal spawns a card instead. The goal is to kill Mom.
With Mom as the goal, you can save yourself a little effort by saving The Bible if you manage to find one, as using it will kill her instantly. But even without it, it's not too hard of a challenge. You can save up more powerful damage and tears upgrades for larger rooms with tougher enemies. If you get an item that increases your hearts, your health still stays the same when you leave the room. But any other passive stat boosts will be removed, with a few random exceptions like Experimental Treatment.
Items are chosen at complete random when you pick up a card, and can be from any item pool