If you have multiple skins for each gun, you would have the option to select however many of those you would like to use in-game. Every time you buy the gun in-game, the gun will be randomly skinned from that pool of selected skins.

Pros

• If you already own a skin or multiple skins for a gun, you won't feel as bad about buying another Battle Pass or another skin that came out that you really like.
• This is ideal from Riot's perspective as it will give players more incentive to keep buying weapon skins even if they already have one or more for a given weapon.
  • Players will have incentive to form a collection of weapon skins that they can continue to build because they can use all of them in each game

Cons

• RIP our wallets

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So yeah I'm basically trying to give myself a reason to buy future Battle Passes because it's fun but I am discouraged because I'm a cheap-ass and already have at least one skin per gun so I feel guilty spending more $ to get more skins when I know I am only going to use 1 per game and the old ones will go to waste since I rarely cycle back through to my old skins.