Malamet Battle Glyph is a uncommon Sorcery card from The Lost Caverns of Ixalan (LCI), collector number 198. Current market price: $0.22 (foil $0.32), TCGplayer market prices via Scryfall.
Choose target creature you control and target creature you don't control. If the creature you control entered this turn, put a +1/+1 counter on it. Then those creatures fight each other.