The Gaster Gang is an AU created by bunnymuse which follows a collection of different versions of Gaster living together in the void. The home they live in is stolen from a reality when an experiment caused a black hole. The only version of Gaster present in the AU which is canon to another is Newtale.
He is a scientist who fell into the void first. He blames himself for everyone being trapped there. Referred to as Wingding, he is the shortest and youngest of the group. The majority of the time, Wingding is trying to find a way out of the void. Experiments going wrong infuriates him and he likes personal space which causes friction between him and Swap.
Underswap Sans and Papyrus are his sons. He was the Riverperson before falling into the void. Swap is extremely optimistic about them escaping the void and takes photos of the rest of the group to show his boys when he comes home. He cooks and takes care of the house. This version of Swap!Gaster is not canon to the Underswap game as that version of Gaster remains unswapped. He hates smoking, swearing and liars but loves hugs.
General of Asgore's army, Fell spends most of his time fighting the 'anomalies' from the positive void. Culling these creatures protect the worlds that spawn them. The rest of the time, he watches TV with B. He is the adoptive father of Underfell Sans and Papyrus. He smokes and swears which often results in him being thrown out into the void by Swap.
Stars is the tallest of the Gasters and is a scientist like Wingding. He is the oldest of the Gasters. He spends most of his time as an assistant to Wingding and reminds him of when he needs to sleep and eat. Outer has a caring and fatherly attitude, similar to Swap but calm rather than energetic. He sees the funny side of experiments going wrong.
Newtale is Bunnymuse's own AU. B or Blindy (or ?????? in the infobox image) tends to not be very active with in the home as he's mostly blind. He used to have a tail and has a damaged soul from a sacrifice.
Swapfell was formerly part of the group through manipulation and deceiving. He was removed after he spiked the drinks of the others Gasters, except Blindy, while Swap was making lunch. He said that it was Swap confusing one of Wingding's chemicals for an ingredient and took Blindy to "find a cure". He then brutally harmed Blindy. Fortunately, Fell recovered from the drugs and saved Blindy. After this incident, Swapfell was no longer in the group and the other Gasters were more careful with who they trusted.