Ob Nixilis, the Adversary is a mythic Legendary Planeswalker — Nixilis card from Streets of New Capenna Promos (PSNC), collector number 206p. Current market price: $2.71 (foil $3.52), TCGplayer market prices via Scryfall.
Casualty X. The copy isn't legendary and has starting loyalty X. (As you cast this spell, you may sacrifice a creature with power X. When you do, copy this spell. The copy becomes a token.) +1: Each opponent loses 2 life unless they discard a card. If you control a Demon or Devil, you gain 2 life. −2: Create a 1/1 red Devil creature token with "When this token dies, it deals 1 damage to any target." −7: Target player draws seven cards and loses 7 life.