As an action, you touch a creature who must succeed on a Fortitude saving throw or have its flesh ripple, grow together, and fuse into a nearly seamless whole.
On a failed save, the target is paralyzed and is forced into a fetal position (if humanoid), with only the vaguest outline of its folded arms and legs visible below the all-encompassing wave of flesh. The target retains the ability to breathe, eat, and excrete. If the sudden transformation would prove fatal to the creature (such as fusing a flying target), the target has advantage on the save.
A creature paralyzed by this spell can use its action to make an Acrobatics or Brawn check (its choice) against your spell save DC.
On a success, the creature tears free of its fused flesh, causing it to take 4d6 slashing damage as its skin rips.
Creatures not composed of flesh are immune, and a shapechanger can revert to its normal form as an action.