It makes your Misty Pokmon deal 20 extra damage to the opponent's active Pokmon, but only if you discard two cards in your hand
All ten of the gold cards with mutate made use of hybrid mana
You can break this effect in something like Neera, Wild Mage by having a bunch of scry effects and expensive spells, but even then it could still easily backfire and kill you
Chaos Defiler Chaos Defiler is your demonic Ravenous Chupacabra, or a demon with a removal spell tacked to it that triggers when it enters and also triggers when it dies
A two-mana 3/1 with lifelink is going to make the cut just to keep your curve efficient more often than not, though thats also true of a two-mana 2/2 with haste for red decks
Konami changes its banned rotation every couple of months, though, so if you land a monstrously strong UR card that you cant put in your deck now, itll probably be un-banned before too long