Whenever all three words of power have been collected for "Ice Form" you can use it to permanently freeze an NPC in place. By default, there is also frost damage applied to the NPC whilst lying on the ground frozen. Therefore, you must pick one of two versions.

1) Permanent Ice Form (added eternal paralysis)

2) Permanent Ice Form - Only Paralysis (Removes frost damage so only the paralysis effect is left, essentially letting you freeze another NPC until you leave or interact with them again)