Tyranids are creatures introduced through Magic's Warhammer 40,000 Commander release. Their cards are concentrated in green, blue, and red and commonly care about +1/+1 counters, X spells, and enormous monsters.
Magus Lucea Kane can copy X spells, while The Swarmlord grows according to how often it has left the command zone. Ravenous creatures further reward pouring large amounts of mana into one horrifying creature.