This content is exclusive to Pixel Gun 3D. It isn't in Pixel Gun World!
Weapons Skins are textures that can be optionally equipped on certain weapons. They can be bought with gems, although they are very expensive. Naturally, every weapon has a texture on them, but some can have multiple texture choices, and only one can be equipped at a time.
Initially, weapon skins were introduced in the 11.0.0 update, but the overall weapon skins system was revamped later in the 16.4.1 update. Originally, in 11.0.0, there were 12 weapons with only one weapon skin for each weapon, and they all have the same skin theme, which is golden. Moreover, these gun skins cost coins instead of gems and required a certain league to unlock them.
The skins that exist in the reskinned weapons would actually aesthetically work on the weapon's original form and vice versa, since the said weapons would usually have the same shape.
It is questionable as to why reskinned weapons exist separately and both the original and the reskinned weapons would have skins each, since the reskinned weapons could be considered as another weapon skin to the original weapon.
The Resort Casanova, the Neon Anti-Champion Rifle, the Chrome Big Fatality Gun, the golden skins and a few other skins are all animated skins.
The Storm Hammer is the only melee weapon to have a skin, ever since the introduction of the weapon skins.