Curse of Origins

This high level curse polymorphs the subject into a more primitive evolutionary form of the race. The target must succeed on an Intelligence saving throw or be bound by the curse, if it succeeds, it is immune to this curse if you cast it again. While affected by this curse, Divination spells can't locate the original target or their origins (because they lost their original identity). Not even a Wish can uncover their original name if the component was destroyed after casting.

Example: A Tabaxi might be a tiger, a human might be an ape, a lizardfolk might be an alligator, etc. Nothing before that, meaning no amoeba or anything unplayable.

Note: If the race doesn't have a more primitive form, this curse will not work due to the missing component. 

The bowl is transformed to clay and paste once it’s cast which must then be destroyed, taking their memories and name for the duration.The recipient of the curse loses their memory of who they are (vague nightmares at best), specifically their name, but they retain their original intelligence, wisdom and charisma scores. They can learn new abilities and level up normally, but they are restricted to what is possible in their new form. For instance, a lizardfolk changed into a lizard won't make a good monk while in that form.

This new shape becomes, for all intent and purpose, their new original form and their “creature type” is shapechanger for the duration (the only clue something might be amiss). Other methods of changing shape do not cancel this curse. 

Unfortunately, the recipient does not emanate a Cursed aura. However, the curse is researchable (one check, no advantage, DC 28) when looking for examples of something like this ever happening before.

Ending the Spell. During the casting of the curse, you can specify a condition that will cause the curse to end and release the target. The condition can be as specific or as elaborate as you choose, but the DM must agree that the condition is reasonable and has a likelihood of coming to pass. The conditions can be based on another creature's name, identity, or deity but otherwise must be based on observable actions or qualities and not based on intangibles such as level, class, or hit points.

A remove curse spell can end the curse only if it is cast as a 9th-level spell and their original name is called out in the casting. This restores their original form, memories, skills and abilities. Anything learned while cursed merges with their past. Conflicts must be decided between at that time, discarded knowledge and abilities are lost but compatible multi-class options may remain. 

Note: You may not double up on Class Paths, Feats, Ability Score improvements or other things that violate the character advancement process. Your DM will help you sort out what stays and what goes. You may have lived a double life for a time, but there's only room for one in the end. If you hated your past, this is definitely a way to replace it.

Designer's Note: This could also be another option for the Imprisonment spell. Hence it not being listed as more similar to Transmutation (Polymorph Other) or Necromancy (Bestow Curse).