Couldn't someone effectively double their hit points by having true polymorph cast on them, and the new form is themself. Because when they drop to 0 hit points, they revert to their original form, with the hit points they had before transformation. And if that would work, would a spellcaster get their expended spell slots back?

Quote from DragonLord4444 >>

Couldn't someone effectively double their hit points by having true polymorph cast on them, and the new form is themself. Because when they drop to 0 hit points, they revert to their original form, with the hit points they had before transformation. And if that would work, would a spellcaster get their expended spell slots back?

 Creature into Creature. If you turn a creature into another kind of creature, the new form can be any kind you choose whose challenge rating is equal to or less than the target's (or its level, if the target doesn't have a challenge rating). The target's game statistics, including mental ability scores, are replaced by the statistics of the new form. It retains its alignment and personality.

it specifies a different creature (it uses “another kind of” here and “different” elsewhere), so no, you could not do this.

Ok, thank you iconarising.