As an action, you create a shard of ice and fling it at a creature within 10 meters. Make a ranged spell attack against the target.
On a hit, it takes 2d8 piercing damage.
On a critical hit, it takes twice as much damage.
On a miss by 4 or less, it takes half as much damage.
Hit or miss, the shard then explodes around the creature. Each creature within 1 meter of that point must make a Reflex saving throw.
On a failure, it takes 2d6 cold damage.
On a critical failure, it takes twice as much damage.
On a success, it takes half as much damage.
On a critical success, it takes no damage.
If the knife strikes a body of water or a liquid that is principally water (not including water-based creatures), it freezes the liquid to a depth of 15 centimeters over an area 1 meter in radius. The ice is an instantaneous effect, but persists as nonmagical ice. Under temperate conditions, the ice lasts 1 minute. Creatures that were swimming on the surface of frozen water are trapped in the ice. A trapped creature can use an action to make a Brawn or Nimbleness check (its choice) against your spell save Difficulty to break free.
You can increase the piercing damage by 2d8 and the cold damage by 2d6 for each additional mana expended.