Ob Nixilis, the Fallen is a mythic Legendary Creature — Demon card from Secret Lair Countdown (SLC), collector number 15. Current market price: $5.46 (foil $10.59), TCGplayer market prices via Scryfall.
Landfall — Whenever a land you control enters, you may have target player lose 3 life. If you do, put three +1/+1 counters on Ob Nixilis.