Molten Gatekeeper is a common Artifact Creature — Golem card from Modern Horizons 3 (MH3), collector number 128. Current market price: $0.21 (foil $1.59), TCGplayer market prices via Scryfall.
Whenever another creature you control enters, this creature deals 1 damage to each opponent. Unearth {R} ({R}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)