The Flock
From Transcendence AU Wiki
The Flock are a herd of demonic sheep, and the remnants of Bill's drove. Technically, they belong to a class of being know as 'nightmares'.
History
The Flock was inherited by Dipper along with Bill's power. It's most likely he first discovered them around the time he worked out he owned his own plot of the Mindscape.
Even after the universe ends, the Flock remains. The influx of new energy released when Dipper restarts everything transforms nightmares, including The Flock, into demons, and the dreams into angels.