Unravelling Dart

A mote of shadow energy leaps toward your foe seeking out its weakness. Make a ranged spell attack against the target. On a hit, the target takes 1d8 force damage.

(Bonus Action): You may take a moment to enhance this spell to seek out your enemies weakness, if you succeed an Arcana check with a DC equal to 12 + (Creature CR / 2). If successful and the creature has any vulnerabilities, the spells damage becomes this damage type and deals additional damage based on that vulnerability.  Once you have succeeded this check the spell will maintain this enhancement for up to 10 minutes, and will effect other creatures of the same type and vulnerabilities.

This spell's damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).