Creature — Nightmare
Ikoria: Lair of Behemoths
84/100
Gains value in 2HG: hits each opponent, symmetrical discard.
There are two opponents in 2HG, so every 'each opponent' clause resolves twice against a single shared life total.
'Each opponent discards' is a two-for-one in 2HG. Syphon Mind and friends jump several tiers here.
Ratings start at a neutral 50 and are adjusted by rules derived from 2HG's structure — shared 60 life, shared turns, two opponents. They'll be recalibrated against real play rates once teams start submitting decklists.
Mutate 
(If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Menace (This creature can't be blocked except by two or more creatures.)
Whenever this creature mutates, each opponent discards a card.