Car Battery: Does not influence the card's effect, activating the active item only once.
Jar of Flies: Expends both the card and all charges with no additional benefit.
Alabaster Box: Causes the Alabaster Box to yield rewards without destroying the item or depleting any of it's current charges.
Blank Card: Teleports Isaac to the I AM ERROR] room of the current floor. This will consume both the Blank Card and the ? Card. If done on Chest or Dark Room, will instead spawn an I AM ERROR shopkeeper.
D1 + Schoolbag: ? card can be duplicated with the D1, allowing for single use items to be repeatedly used on effectively a 4 room charge.
Diplopia: Duplicates all pedestal items and pickups in the room, without expending Diplopia.
If used with another ? Card dropped on the floor in the room, allows for infinite duplication.
Glowing Hour Glass: Since the card replicates the effect of moving back one room to the previous state, Isaac keeps the card having not used it as an item until the room later. This effectively gives him charge-free uses of the Glowing Hour Glass.
The card is no longer refunded.
Tarot Cloth: ? Card is used twice, giving the active item the same effect as if Isaac had Car Battery.
The interaction with Blank Card presents a paradox, as Blank Card and ? Card try to replicate the effects of each other. This would result in an endless loop, so a special case was put in.
The Blank Card interaction is one of the four reliable ways to reach the I AM ERROR room in game, alongside Teleport 2.0 in certain circumstances, using Red Key to go beyond the 13x13 level grid, and Undefined.