Black Ice Shatter

As part of the action used to cast this spell make a melee attack with a weapon against one creature within the spell’s range. On a hit the target suffers the attack’s normal effects and shards of black ice break from the target and linger in a 5 feet radius around the creature hit. If another creature passes this space it takes cold damage equal to your spellcasting ability modifier. The shards disappear afterwards. If at the start of your next turn no creature was hit, deal half the damage rounded up to your initial target instead and end the spell's effect. This spell’s damage increases when you reach higher levels.

At 5th level, the melee attack deals an extra 1d8 cold damage to the target, and the cold damage from the shards increases to 1d8 + your spellcasting ability modifier. Both damage rolls increase by 1d8 at 11th level and 17th level.