Rime Spell

The material below is Open Game Content from a 3PP Source

Rime Spell (Metamagic)
Creatures damaged by your spells with the cold descriptor become entangled.
Benefit: The frost of your cold spell clings to the target, impeding it for a short time. A rime spell causes creatures that takes cold damage from the spell to become entangled for a number of rounds equal to the original level of the spell.

This feat only affects spells with the cold descriptor. A rime spell uses up a spell slot one level higher than the spell's actual level.