Spectrum Sentinel is a uncommon Artifact Creature — Soldier card from The Brothers' War (BRO), collector number 244. Current market price: $0.44 (foil $2.30), TCGplayer market prices via Scryfall.
Protection from multicolored (This creature can't be blocked, targeted, dealt damage, enchanted, or equipped by anything multicolored.) Whenever a nonbasic land an opponent controls enters, you gain 1 life.