Skinspawn. When the Forsaken Shell kills a medium or smaller sized living humanoid creature, at the start of the Forsaken Shell's next turn that creature's skin peels from it's body and rises as a new forsaken shell.

Unconventional Movement. The Forsaken Shell can not be flanked.

Flexibility. The Forsaken Shell is immune to any effects that would forcefully move it in any direction. 

Skin Slap. Melee Slam Attack: +8 to hit, reach 5 ft., 1 target. Hit: 9 (1d8 + 5) bludgeoning damage and 5 (1d10) necrotic damage.

A successful strike with Skin Slap heals the Shell for 5 (1d10) HP, and also grapples the target. In addition to damage dealt, this attack also drains 1 Hit Die from the victim’s Hit Die pool.

Envelope. Melee Attack: always hits, targets creature grappled.

The target of this attack must make a grapple check against the Forsaken Shell. The Shell gets +8 to this check.

If the target fails to beat the roll of the Shell, the target is totally enveloped by the Forsaken Shell, and takes 16 (3d10) necrotic damage. The Enveloped target moves at half its speed, and can take no action other than trying to break free with an Athletics or Acrobatics check made against the Shell.

While enveloping a target, the Forsaken Shell can take no other actions. At the beginning of each of its turns, it deals 16 (3d10) to the target it is enveloping.

This damage also heals the Forsaken Shell for 5 (1d10) HP, and drains 1 Hit Die from the Hit Die pool of it’s target.

If the Forsaken Shell takes damage from any melee attack, or lightning spell, the creature it is enveloping takes 50% of the damage taken by the Forsaken Shell.