Any cards, damage, effects, or special conditions on the original Pokmon (which you discard but does not count as being Knocked Out) now moves to the new Pokmon
Notably, if you cast Murder targeting your opponent's Mirrorwing Dragon, your creatures will each get a Murder, not your opponent's
(If a creature has multiple instances of prowess, each triggers separately.) Whenever you cast a noncreature spell, target creature you control can't be blocked this turn
Decks like Raging Bolt and Gholdengo can make use of this card to get energy back to set up for attacks on the following turn, which helps them maintain consistency after their board is broken
With most equipment decks winning in an ostensibly fair way (through creature combat), I dont see these being as egregious as tutoring for a combo
The main reason I have it at the top of this list is down to how front loaded the card is