Jacob and Esau can use this item to duplicate an active item to each have the same active item.Using Diplopia on another copy of Diplopia will not work.Multiple copies of the same item do count towards transformations.Picking up multiple copies of items that can cause Isaac to transform will not count towards transformation progress.The original items will still behave as normal: once an item is chosen, the others will disappear. If used in an Angel Room that has multiple item pedestals, the duplicated items can be taken for free.The original items will still be offered at an HP price, and Deal with the Devil precedent will not be obtained. If used in a Devil Room or the Black Market, the duplicated items can be taken for free.However, this allows Isaac to essentially take both items. If used in a Treasure room on the alternate path, only one duplicate can be taken.If item pedestal that is duplicated is visable as "?" (for example with the Curse of the Blind), duplicate will be visable as "?" until taken, just like the original item pedestal.If used on the The Polaroid and The Negative after defeating Mom, the duplicates can be taken without affecting the originals.Taking one of the original items does not cause the duplicates to disappear. If used in the Boss Rush room, all available items will be duplicated and all the duplicates can be taken ( this will still start the Boss Rush) however, only one of the original items may be taken.If used in a Shop, the duplicated pickups and items can be taken for free.
Using Diplopia on an empty item pedestal will spawn another random item.Using Diplopia on a trinket does nothing.Using Diplopia on a trinket will spawn another random trinket instead of duplicating the trinket.Duplicates all pickups and pedestal items in the current room, then disappears.