There's been some debate regarding the Rare The Collector from Guardians:
The Collector-Taneleer Tivan:
While The Collector is active, once per turn, you may pay the Purchase Cost of target unpurchased character die minus 2 (to a minimum of 1). If you do, field that character die at level 1. Return that die to its owner's card at end of turn or when it leaves the Field Zone.
The text "Return that die to its owner's card..." implies that one could target an opponents character die. Does The Collector allow you to target your opponents characters?