"You can't hide me away forever, Undyne! I'll aaaalllwwwaaayys be here! UNTIL THE END OF TIME!"-S. Dayye

S. Dayye, also known as Sonny Dayye, is a demonic entity, summoned by Undyne when she was a child.

Ownership and Credits

hOi! I'm Aidan, this is mine! Also, thanks to Alex Hirsh and Toby Fox for the inspirations!


S. Dayye is two-dimensional Boss Monster, capable of travelling across time and space. Well, when he's summoned, at least. For thousands of years he laid dormant, until Undyne was dared to summon him. Using the ancient ritual of putting four "masks" (actually his faces) on a pentagram, and lighting a picture of the summoner on fire, before Undyne's very eye, the demon appeared. Undyne quickly undid the ritual, however, it was too late, and he still lingers, sometimes appearing to be a helpful guide or vengeful jerk.


Although it is unknown of the extent of his powers, many abilities have been shown. For one, he can shoot lasers. He can unleash large blasts of energy, and summon large, homing spikes from his eyes.

In Game

He does not appear in game much, but, he does, at least.

  • He will appear in Snowdin. He will babble about cats and bunnies before walking into the woods.
  • He will appear briefly in the Undyne Lost Soul battle, and with his masks too.


S. Dayye will appear as a Boss Monster wearing a grey jacket and grey hat. His eyes are bright red, and said eyes have black streams connecting them to his mouth. He also wears a small, yellow triangle belt buckle, attached to a belt, which hold up his black sweat pants. He wears no shirt, showing his ribcage and two spines, which, are not connected, making a sort of "O" shape.


S. Dayye is mysterious, zany, flirty, and quite devilish. He shows a strong, love-hate bond with Undyne. However, underneath, he is a loving, apologetic man.


  • He seems to know Lindsay Kingsland, and has good-enough relationship with Orion that he can call him "Onion".


  • Yes, he was inspired by Bill Cipher.
  • His masks were inspired by W. D. Gaster's face and Majora's masks.
  • He is not a demon. He is a daemon.