Ouroboroid is a mythic Creature — Plant Wurm card from Edge of Eternities Promos (PEOE), collector number 201p. Current market price: $33.75 (foil $37.68), TCGplayer market prices via Scryfall.
At the beginning of combat on your turn, put X +1/+1 counters on each creature you control, where X is this creature's power.