Jetmir, Nexus of Revels is a mythic Legendary Creature — Cat Demon card from Streets of New Capenna (SNC), collector number 312. Current market price: $10.75 (foil $13.28), TCGplayer market prices via Scryfall.
Creatures you control get +1/+0 and have vigilance as long as you control three or more creatures. Creatures you control also get +1/+0 and have trample as long as you control six or more creatures. Creatures you control also get +1/+0 and have double strike as long as you control nine or more creatures.