basically, it's an undertale remake with some older AU's, tweaks, and a lot more, think of it as undertale B&P if the creator wasn't a pdf file and it was better. it's supposed to be nostalgic, when there weren't as many AUs so last breath is canon in this universe, and to trigger it, you have to find the gaster room during a genocide route and then beat the game, then do ANOTHER genocide route. to unlock underfell, you need to do a pacifist/neutral route and kill flowey after the omega flowey fight, then you can access underfell on the title to unlock underswap you have to beat the game on mirror mode (which will be a gamemode that makes all rooms and battle mirrored) to trigger disbelief, you have to do a genocide route, kill sans, then immediately reset and do another genocide route, you'll find sans in snowdin then you can go fight papyrus to trigger distrust you just have to do what you would do to trigger disbelief in underswap lol to trigger dusttale you need to do a genocide route 3 times to do it to trigger bustbelief you need to trigger dusttale, then trigger disbelief To trigger promised you need to press A minor on a guitar, then reset and do a genocide run
Give me some other ideas also I'm not making you do 92305702157904 genocide routes for disbelief or LB also you can ask to join the team I guess
