Paralyze
Enchantment — Aura
Enchant creature
When this Aura enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.
At the beginning of the upkeep of enchanted creature's controller, that player may pay 
. If the player does, untap the creature.
Anson Maddocks
Rulings
This is a change from the most recent wording. As was the case in the past, Paralyze itself has the last triggered ability, rather than granting that ability to the enchanted creature.
(wotc • 2007-09-16)
The creature can only be untapped using Paralyze once per turn.
(wotc • 2004-10-04)
Paying the cost is optional.
(wotc • 2004-10-04)
Two Paralyzes are not cumulative. Paying either one will untap the creature.
(wotc • 2004-10-04)
Paralyze can be cast targeting a creature which is already tapped.
(wotc • 2004-10-04)
Rulings
This is a change from the most recent wording. As was the case in the past, Paralyze itself has the last triggered ability, rather than granting that ability to the enchanted creature.
(wotc • 2007-09-16)
The creature can only be untapped using Paralyze once per turn.
(wotc • 2004-10-04)
Paying the cost is optional.
(wotc • 2004-10-04)
Two Paralyzes are not cumulative. Paying either one will untap the creature.
(wotc • 2004-10-04)
Paralyze can be cast targeting a creature which is already tapped.
(wotc • 2004-10-04)