Skins are the best thing for customization in Mitos.is, but they only work in some games, so team skins replace them. A lot of them are like the ones you see it Agar.io, but others are made from Mitos.is itself. Custom skins can be made, but the more pixels, the more money it cost.
Inside The Skin Editor
this Dude's Custom Skin
The Best Skin
Mitosis-How to Make and use a Custom Skin