False Memories AU/FicRecs
From Transcendence AU Wiki
Untitled by avafalls (mod A) (link)
What about heartwrenching headcanon? What if Dipper actually died during the Transcendence, but Bill got weakened a lot and was imbued with Dipper's memories, feelings and will to the point he actually thinks he's him...until, years later, he finds Dipper's reincarnation.