Level drain can be great. I had 2 players that were young silver dragons. They polymorphed into humans to lead a raid against a cult and their humans were all wiped out while they escaped. They tried shifting back and couldn't. Bahamut trapped them in their forms until they learned what it was like for them and maybe they'd be more careful with their lives the next time they meddled in their affairs. They've gotten moments where they got to transform during intense moments and the end of their arc will be the ability to transform again (they're druids). It has been incredible and there are some really fun mechanics with it. It can just be hard to do if the mechanic you are unlocking is Power Word Kill or something because at that point all you are mechanically doing is getting high level again and feeling weak until then. I don't like that way of doing it. Gale doin something foolish in his youth to "Notice me, Senpai" Mystra even though he was wildly out of his depth, regardless of aptitude, would be a more appropriate arc to pursue. Its always just a bit off for some reason with their stories haha.
I hace a concept for a draconic sorcerer who is actually a young black dragon stuck in a form somewhat close to a drow (or wood elf fluffed as drow). Her dragon form is heavily damaged and scarred and it involves great pain for her to enter it. (as a hatchling she'd been tortured by goblins and accidentally saved by adventurers.) Some of her spells represent briefly returning to draconic form. Like polymorph to a T-Rex would be T-Rex stats but fluffed as a dragon with damaged wings and the mental stat drop due to the pain she'd be in.
She was a bit on the shy and hesitant side. Got the idea from a story a while back. I figured if she were to get to Epic Levels, some of the Epic Boons would be things like "Ageless" and her 9th spell would be Shapechange.
