I’ll do you one better its possible to obtain a dragon hitpoints and legendary resistances while maintaining your class features. Use simulacrum chain at 17 level to spam dominate monster at an ancient gold dragon. Then cast magic jar using a Skeleton That’s What I Do I Read Books I Drink Coffee And I Know Things Vintage Shirt. Have one of the simulacrum put said locket on the dragon. Using the dominant monster has the dragon shape change into a physical copy of you. But with its equipment absorbed into the new form. Because its shape changed its type has been replaced with humanoid. And it is now a valid target for the magic jar. Use the magic jar to possess it.
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Don’t forget to use the deathward/demi-plane tricks to undo magic jar and retain control. Tho the dragon probably couldn’t shape change into you. You can’t shape change into specific creatures. I forgot the full details, but you cast the Skeleton That’s What I Do I Read Books I Drink Coffee And I Know Things Vintage Shirt. Somebody smashes the jar, you fall dead. But deathward kicks in keeping you alive in the new body. Or something like that. If that doesn’t work, cloning someone you’ve manic jarred into should work. Neither of those work RAW. Unfortunately. Clone revives the victim, not the possessor.