Your body and soul are bound to a fiendish plane
of existence. You have disadvantage on death
saving throws as the plane attempts to pull you
back to it. If you would be killed, your soul has
been dragged back to a plane of existence of the
GM’s choice. This plane is your new home, and
you become an NPC under the GM’s control.
If you are on the fiendish plane responsible for
your transformation, this flaw has no effect.