Monster Kid

Monster Kid was the adoptive child of Asgore and Toriel.

But one day, something terrible happened to him and the fallen child.

Story
Their dialogue is present in Waterfall. Judging from said dialogue, Monster Kid doesn't seem to change much from his Swap-counterpart, as he still helps Frisk after their fall.

Monster Kid refers to Frisk as "another kid Toriel has taken in." This could mean that Monster Kid and Frisk aren't the only ones to have been taken in by the Dreemurrs.

Appearance
Monster Kid eyes are seen to be closed with purple bags under his eyes. He wears a purple robe of some sort. His robe has a light purple heart in the middle, which has a Delta rune symbol. They also wear no shoes.

Personality
To Be Added...

Frisk (Adoptive Sibling)
Frisk was the adopted sibling of Monster kid before they died.

Asgore (Adoptive Father)
To Be Added...

Toriel (Adoptive Mother)
To Be Added...

Asriel (Adoptive Brother)
To Be Added...

Trivia
TBA