This is an old project I never finished, the Elementalist System.
Every player would choose one of the four elements to gather proficiency, only one.
After beating monsters and achieving objectives related to the Element Questline, the player could unlock 3 Skills.
One of them would transform itself in a temporarily form, like the GIF, which his skin color, clothes colors, hair color, effect and aura would change.
While the transformation lasts (which should have a huge cooldown), buffs were applied, each element with it's own unique benefits and weakness.
The Elementalist also have a companion that should be grown according to it's power.
You can see the Wind counterpart here
This work is from about 4 or 5 years ago, It could be way better, since there's Alpha Effects and better sprites, but I'll leave it here as a Showcase anyway.
Interested on anything similar?
Drop a PM on my rAthena Profile
. I'm open to commissions.