Crystal needle

Create 3 needles made of crystals. Each needles can targets a creature of your choice. On hit the needle inflict 1 piercing damage and stay in the target. Once 7 needles have hit the target without being remove they explode inflicting 1d8 of force damage. The needles can be remove using one bonus action but doing so inflict 1 slashing damage for each needles remove. 

At lvl 5:The explosion inflict 2d8 of force damage.

At lvl 11:The explosion inflict 3d8 of force damage and the needles inflict 2 piercing damage on hit and 2 slashing damage upon removal.

At lvl 17:The explosion inflict 4d8 of force damage and the needles inflict 3 piercing damage on hit and 3 slashing damage upon removal.