The Glock Fade is currently the rarest and most expensive of all Glock skins in CS:GO.

The iconic StatTrak!" M4A4 | Howl is possibly the most expensive CS:GO skin and certainly the rarest. It's a contraband skin (the only one of this rarity), which means that you can't get it by opening cases anymore. In fact, the only way to obtain the Howl is through trading it with other players on skin marketplaces.