Echo's Acid Darts (UPDATE)

you summon 5 Darts that each target a creature of your choice and explode on impact. make a ranged spell attack doing 1d8 acid damage on a successful hit or 1/4 as much on a miss (rounded up).  at the end of the creature's turn they take 4d4 acid damage, then 3d4 on their next turn, then 2d4, then 1d4. on a miss they don't take the extra damage. 1 creature can only have one of the extra damage effect at a time.