Extremely, extremely late, I know, but it's useful to compare how the Kickstarter characters were portrayed in-game.
The furry dragonkin is stuffed deep into a secret, out-of-the-way area of the game that is completely missable by a regular player. On top of that, they can only be met on a single day of the year in a single
hour of that day.
Even then, their character is not properly named in-game, and is merely referred to as "So Sorry" so no-one searches the character name and gets horrible fetish art.
So Sorry is a hidden miniboss the protagonist encounters in the Art Club Room. He was a bought-in character during the Kickstarter for the game. The protagonist must read the sign in the Art Club room when the computer's clock is set for October 10th at 8 PM (i.e. between 8:00 and 8:59) to...
undertale.fandom.com
There's another hidden Kickstarter character, but it's basically guaranteed to appear if you're trying to figure out the secret room mushroom 'puzzle' for any length of time.
Glyde is a hidden monster the protagonist can encounter in Snowdin Forest. It was designed by Mike Reid as a bought-in character during the Kickstarter for the game. In order to encounter Glyde, the protagonist must go to the Mysterious Door room outside Snowdin (with the four mushrooms), and...
undertale.fandom.com
The last character is Muffet.
Yes, the hugely popular, main route boss with her own full themed area was a Kickstarter character too.
Interesting to see in comparison how Toby treats them in-game.