Coats of many colours...

I decided to do my own sprites of the sprited works by Male-Gardevoir.

If a Burmy is levelled up in the nesting place of any four of the following legendary birds - Ho-oh, Lugia, Articuno, Zapdos - it will create a cloak of their feathers and, when it evolves gain their primary elements as its secondary element (bug/fire, bug/psychic, bug/ice and bug/electric).

A flying forme doesn't make much sense since Mothim already exists.
And a water forme makes even less sense since bagworms aren't able to survive in such conditions. That's the main reason why Wormadam should have Articuno and Ho-oh feathers instead of, say, fire/coal or snow/ice covering it since the bug type is weak against these two types.

I also thought of making a Honchkrow-feather cloak forme (bug/dark) but it didn't really fit in with the rest..

Ho-oh plumage cloak wormadam was originally created by G-FauxPokemon whose work is found here...
Articuno, Zapdos and Lugia plumage cloak formes are originally made by this guy
Plant, Sandy and Trash Cloak formes are by the Pokemon Company, Nintendo.