LiverIceCream My in-game player character is a skeleton mecanim. Would the same principles in the Mix and Match example apply, or would it need a completely different solution? I wondered this because the OptimizeSkin method is set up for a skeleton animation. I'm not sure if there's a difference in how they handle skins, so I wanted to check before setting it all up.

SkeletonAnimation and SkeletonMecanim are both subclasses of SkeletonRenderer. SkeletonRenderer handles everything skeleton-related except animation. So it does not matter which animation system is used when changing skins.

LiverIceCream Assuming it will work with a mecanim - could I get the for dummies version of how to tell the skeleton mecanim in the player prefab that it should use the skin that was generated in the character creator? I've tried to figure this out myself, but I'm a little out of my depth once I get out of Spine and into C#.

I assume you're using SkeletonAnimation in what you call character creator above. If your game logic combines selected skins and assignes it to the SkeletonAnimation object, your game logic should anyway store the selected combination of skin items as a game state somewhere. You don't want to lose the information when e.g. contionuing to play the game the next day. Then just combine the same skin items again and apply it to the SkeletonMecanim GameObject.