Sylvar's Biting Blade

The next time you hit a creature with a weapon attack within one minute of casting the spell, your weapon glitters with Hoar Frost as you strike. The attack deals an extra 2d6 cold damage to the target. Additionally, if the target is a creature, it must succeed on a Constitution saving throw or it's movement is halved until the end of it's next turn. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the extra damage increases by 1d6 for each slot level above 2nd.