Enchantment - Aura, 2U (3) Enchant creature At the beginning of the upkeep of enchanted creature's controller, that player sacrifices that creature unless he or she pays {2}. When Slow Motion is put into a graveyard from play, return Slow Motion to its owner's hand.1
Illus. Todd Lockwood
You can use abilities of the creature during upkeep before dealing with the cost this card imposes. [Urza's Legacy FAQ 1999/02/03]
You choose whether to pay or not on resolution. If not, then you sacrifice the creature. You can choose to not pay if you no longer control the creature on resolution. [D'Angelo 1999/06/01]