The Chains of Undead

When the caster hits the target, the caster rolls 1d20 with no modifiers. With a result of 15 or higher, the chains degrade immunities to resistances, degrade resistances to no damage negation, and increase the damage multiplier for anyone without any damage resistances or immunities to 1.125x normal damage, rounded to the nearest whole number. On a result of 14 or lower, the immunities and resistances stay the same. When hit on a creature with Necrotic damage immunity, the creature is given the restrained effect until either killed by outside sources or breaks free.

These chains also give the restrained condition and only disappear when one of the following happens;

1. Target dies

2. Caster dispells the spell.

The Chains of Undead deals a character-level amount of creature CR + Spell Slot Level (example = 8d12 + 4) at the start of every round. To escape these chains, the creature locked inside must make a DC 27 Strength saving throw. The DC increases by +2 for every level above 4th. 

Upon breaking the chains, the creature takes 2d10 piercing damage + 2d4 bludgeoning damage + 1d8 necrotic damage and gains 1 level of exhaustion.

Every round, the hitpoints the creature loses while restrained by the chains, any form of damage the caster is healed for, and/or can spread amongst their teammates as they wish. Any overflow of hitpoints goes into temporary hitpoints for 12 hours, regardless of whether the creature being restrained in the chains is dead or alive.