You discovered that ghost has resistance to fire, lightning, thunder damage. A few high rolls from me and Tobias is in danger right now so I decided to drop you a helpful hint below.
Unless anyone correct me your locations at the start of enemy turn will be following
Hint: at least those of you who know high level magic would know
[ +- ] Damage to creature under Polymorph spell
In DnD if a creature is transformed into another and that another creature HP drops to 0 transformation ends and original creature takes the left over damage, but it isn't knocked unconscious. Be it a spell or feature such as wildshape. The same will apply here