Heartseeker (DST) from Darksteel, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Michael Sutfin
• Card Text:
  Equipped creature gets +2/+1 and has “T, Unattach Heartseeker: Destroy target creature.”
  Equip 5 (5: Attach to target creature you control. Equip only as a sorcery. This card comes into play unattached and stays in play if the creature leaves play.)