Artifact — Equipment, 2 (2)
Uncommon
Equipped creature has first strike and "{T}, Unattach Surestrike Trident: This creature deals damage equal to its power to target player."
Equip {4} ({4}: Attach to target creature you control. Equip only as a sorcery. This card enters the battlefield unattached and stays on the battlefield if the creature leaves.)
Illus. Ben Thompson

12/1/2004: Surestrike Trident grants an ability to the equipped creature.
12/1/2004: The equipped creature's controller chooses whether or not to activate the activated ability. It doesn't matter who controls Surestrike Trident.
12/1/2004: "Unattach Surestrike Trident" means just that -- Surestrike Trident moves off the creature it was equipping and remains on the battlefield.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern