Butters
Butters is a promotional release. Butters is an Intro Line Wild Species Super Duper Rarity Class. In other words, Butters card and t shirt is the equivalent of packing a Blastoise in a pokemon booster pack back in 1999. As we continue to release Dupes, you will become more familiar with the breakdown of characters and their corresponding Rarity classes.
Keep in mind that as the Duperverse continues to unveil itself, NOT ALL dupes will be available to purchase. Some will have to be earned, packed, or rewarded through different incentives. Members can only purchase shirts of Dupes they have in their Duper-deck.
Butters is unlike what you will typically see here. He belongs to a greater class of Duperhero. These will be released on a longer time scale, as everything is connected and the greater the hero, the greater the process behind revealing them. Butters slipped through the cracks and got in the walls as cats are known to do.