"A developer who got fired once said she was very nice and helpful."
Not much to say I guess. 5 cost so you can try and combo it to keep it alive. 12 health since it's meant to be played against a board worth stealing. Similar to Doomsayer and Validated Doomsayer in principle, obviously; tried to keep their balance in mind a little though the nature of the effects are pretty different. xP
Art's from the Kaladesh reprint of Diabolic Tutor from Magic the Gathering.
(EDIT: Just a slight tweak to the text's wording. Effect's the same.)
Can be used to move debuffs such as Corruption, Humility, Barnes 1/1 debuff, or freeze effects to other less valuable minions. Also great for passing an attack buff to another minion that hasn't attacked, moving important effects to minions with more health, and moving "Can't Attack" effects to other characters!
Or it can be used to give bad effect to your opponent. Using this on Ancient Watcher not only get rid of its Cannot Attack, but you also make an enemy minion unable to attack. Use it on Ticking Abomination, you give your opponent a ticking time bomb that threaten to blow his board up!
Do note that, it only swaps card texts but not Attack or Health. A vanilla Lich King is still a 8/8 that needs answer, and the enemy minion is chosen randomly so you may end up swapping card texts with something lousy like a Silver Hand Recruit. It costs 2 Mana which is pretty low, but to maximize this card's power, you need to run a bunch of otherwise weak cards that weaken your deck, so I feel it's pretty justified.