How come my bulbasaur wont evolve?

Question

In Pokemon go I have a bulbasaur with yellow around its head and I have more than enough bulbasaur candies and stardust to evolve it but it doesn't give me the option to evolve it like the other bulbasaurs I have caught previously.

Answer 1

You have the Shedinja-Costume Bulbasaur.

Shedinja-costumed Bulbasaur cannot evolve.

Source

Comments

It was a Fall Event Pokémon, like Yamask-Costumed Squirtle, Cubone-Costumed Charmander, and Mimikyu-Costumed Pikachu.