Names

At the beginning of Undertale, the player is given the choice of naming the fallen child. Although this is depicted as the player naming the main character, it is in fact naming the first human to have fallen into the Underground. Certain restrictions as well as special cases occur if specific names are selected.

Names disallowed (not case sensitive)

 * Sans - "nope"
 * Toriel - "I think you should chose your own name my child"
 * Asriel - "..."
 * Asgore - "You cannot"
 * Flowey - "I already CHOSE that name"
 * Undyne - "Get your OWN name!"
 * Alphys - "D-don't do that"
 * Gaster - reloads intro sequence before you can select

Names with custom responses (not case sensitive)

 * Frisk - "Warning: this name will make your life hell. Proceed anyway?" [The game enters Hard mode]
 * Murder/Mercy - "That's a little on-the-nose, isn't it?"
 * Catty - "Bratty! Bratty! That's MY name!"
 * Bratty - "Like, OK I guess"
 * Temmie - "hOI!"
 * Aaron - "Is this name correct? ;)"
 * Woshua - "Clean name."
 * Chara - "The true name"
 * AAAAAA - "Not very creative...?
 * METTA - "OOOOOH!!! ARE YOU PROMOTING MY BRAND?"
 * Jerry - "Jerry."
 * Papyru - "I'LL ALLOW IT!!!!"
 * Alphy - "Uh.... OK?"
 * Napsta/Blooky - "............ (They're powerless to stop you.)"
 * Bpants - "You are really scraping the bottom of the barrel."
 * Gerson - "Wa ha ha! Why not?"
 * Shyren - "...?"