Skin Concept: Monarch Kha'zix
The idea is kha'zix starts the game retextured to look like a caterpillar. In this case the swallowtail caterpillar:
https://c2.staticflickr.com/4/3273/2747294669_9369be02fd_b.jpg
When he evolves his wings (complete with new cocoon transformation animation) he gets butterfly wings and is textured to look like the swallowtail butterfly:
http://cdn.phys.org/newman/gfx/news/hires/2011/ataleofmoret.jpg
Similar to Guardian of the Sands Kha'zix, evolving your ult makes you look "deadlier". Evolving your ult before wings retextures kha'zix into the pipevine swallowtail caterpillar:
https://upload.wikimedia.org/wikipedia/commons/7/75/Pipevine_Swallowtail_larva,_Megan_McCarty52.jpg
Evolving wings and ult retexture Kha'zix to look like the pipevine swallowtail butterfly:
http://www.gardenswithwings.com/uploads/images/db/piswMCde.jpg
Accurate or not also remodel his antennas to be curly and give him long eyelashes.
I didn't mention any special particle changes because Kha'zix needs a cheap skin q_q
rito pls