Krenko, Tin Street Kingpin is a rare Legendary Creature — Goblin card from War of the Spark Promos (PWAR), collector number 137p. Current market price: $3.35 (foil $14.16), TCGplayer market prices via Scryfall.
Whenever Krenko attacks, put a +1/+1 counter on it, then create a number of 1/1 red Goblin creature tokens equal to Krenko's power.