Yet Another Swapping AU, or YASAU is an AU created by GoldenDust66. As the name implies, it's another swap AU.
Frisk is identical to Undertale, just she's now female instead of genderless.
Mettaton box form takes the Empty One Role. He tries to trick you with 'friendliness hearts' with are actually harmful bullets.
Chara takes the Caretaker Role. She lives in the Ruins, and contacts Asriel whenever possible, thanks to the Ruins' Wifi.
Sans takes the Recluse Role. You find him in the Ruins, lying on the floor. He likes making puns.
Undyne YET AGAIN takes the Judge Role! She lives in Snowdin with Alphys.
Alphys takes the Ambitious Role. She tries to capture Frisk throughout Snowdin.
Asgore takes the Idolizer Role. Here, he is much younger and wants to see Gaster in battle.
Gaster takes the Captain of the Guard Role. He uses magic hands to attack Frisk throughout Waterfall.
Monster Kid takes the Royal Scientist Role. He is the creator of Papyrus's robot body.
Papyrus takes the Celebrity Role. He is the sole star of the Underground.
Asriel takes the Monarch Role. He rules over the Underground, but often gets help from Chara.
Mettacrit is Mettaton as a ghost, and he takes the Fallen Angel Role.
Napstablook takes the Fallen Role. He possesses you at the end of a Genocide Route.
W. D. Toriel
Toriel takes the Forgotten Scientist Role. Not much is known about her.