There appears to be a minor bug of missing Tychus “Power Drench” skins. The “Arctic Power Drench Tychus” for example is missing for purchase.
Similar thing happened during one the last major patches, I think when Hogger was added to the game. Leoric’s Phantom and several mounts and other skins went missing as well, and a weird white and pink Ghost Speeder was randomly added to everyone’s accounts.