heres all the name easter eggs i could find:
FRIEND (or IMAGE_FRIEND/DEVICE_FRIEND)
Battat, Pluey, or Jongler
Mike
Sans
Papyrus
Gaster
Kris
Susie
Ralsei
Player
Name
Starwalker
Seek
JaruJaruJ
CammyboiG
Andrew Cunningham
Forgotten Man
Carol
Noelle
Dess
Seam
Jevil
Spamton (or Spamton G Spamton)
Tenna (or Mr. (ant) Tenna)
Jackenstein
Toriel
Asgore
Undyne
Alphys
Flowey
King
Queen
Tasque Manager
ERAM
Shadow Mantle
Ramb
Gerson
If theres any more or i got something wrong let me know!!