Elukron's Arcane Shackles

You place arcane shackles on a creature that you can see within range. The target must succeed a Wisdom saving throw or become magically shackled. When the shackled target casts a damaging spell, you can use your reaction to reduce its damage by 1d4, and charge your Arcane Barrier (if active) by the amount of damage reduced. Arcane Barrier gains hitpoints equal to twice the spell level only on initial cast. Arcane Shackles have no effect on non damaging spells.

At Higher Levels. When you cast this spell using a higher spell slot, you add 1d4 damage reduction and hitpoints to your Arcane Barrier (if active).