Surestrike Trident is a uncommon Artifact — Equipment card from Darksteel (DST), collector number 147. Current market price: $1.54 (foil $5.89), TCGplayer market prices via Scryfall.
Equipped creature has first strike and "{T}, Unattach Surestrike Trident: This creature deals damage equal to its power to target player or planeswalker." Equip {4} ({4}: Attach to target creature you control. Equip only as a sorcery.)