Clear out the cell. Bring in the next prisoner.

The List

Prison Term

Enchant creature
Enchanted creature can't attack or block, and its activated abilities can't be activated.
Whenever a creature an opponent controls enters, you may attach Prison Term to that creature.

Commander 2011

Enchant creature
Enchanted creature can't attack or block, and its activated abilities can't be activated.
Whenever a creature enters the battlefield under an opponent's control, you may attach Prison Term to that creature.

Magic Online Theme Decks

Planechase

Enchant creature
Enchanted creature can't attack or block and its activated abilities can't be activated.
Whenever a creature enters the battlefield under an opponent's control, you may attach Prison Term to that creature.

Shadowmoor

Enchant creature
Enchanted creature can't attack or block and its activated abilities can't be played.
Whenever a creature comes into play under an opponent's control, you may attach Prison Term to that creature.