Tattermunge Duo is a common Creature — Goblin Warrior Shaman card from Shadowmoor (SHM), collector number 218. Current market price: $0.11 (foil $0.55), TCGplayer market prices via Scryfall.
Whenever you cast a red spell, this creature gets +1/+1 until end of turn. Whenever you cast a green spell, this creature gains forestwalk until end of turn. (It can't be blocked as long as defending player controls a Forest.)