V's Volts

you hold a 1/2in diameter ball bearing in one hand and toss out a pile of metal dust into the air as a loud zapping sound along with slow arching bolts of lightning extend out from you in a 30ft radius for up to 5 rounds or until you lose concentration. Any hostile creature that enters or starts its turn in the spell must make a dexterity saving throw or take 4d8 + spellcasting modifier, it has its speed reduced by half, and it cant take reactions, on a success they take half damage and suffer no other effects.