Calm down please ;)
I agree with H-Shark. Even it's not official, SlitherPlus is very popular...
It seems that four extra skins diseappeared for whatever reason. But much more extra skins are now available ^^
Third batch skins or, more simply, extra skins, are skins available on only SlitherPlus. If you don't have this extension, you can't get the extra skins.
Wiki Logo - I like the actual logo (Slither.io logo)