Honestly, a Mew is easily one of the best fictional species to get turned into. As a Mew, you would have an entire novel's worth of powers and benefits.

Personally, if given the choice of any fictional species to be turned into, a Mew is near the top of my list. Especially if it is lore accurate and filled with common and personal headcanons about them and their powers and abilities.

List of benefits:

1. Psychic powers.
2. Adorable.
3. If for whatever reason you get tired of you form, you can temporarily adopt another. Changing species like a person changes clothes would be fashionable ~

Flying psychic pink cat fetuses are the best!