Undyne's Letter is a letter that Undyne gives to the protagonist to deliver to Alphys in the True Pacifist Route. After the protagonist delivers the letter, Alphys engages in a date with the protagonist.
Undyne gives the protagonist Undyne Letter EX as a replacement if the protagonist throws the original letter away. Undyne Letter EX cannot be thrown away or sold at the Tem Shop.
- You tried to open the letter, but... It's been shut so tightly, you'd need a chainsaw in order to open it. [Use]
- Undyne: OH MY GOD!! I'M GONNA FREAKIN' KILL YOU!! [Use in Snowdin]
- Maybe if you check the lab door, you can slide it underneath... [Use in Laboratory Entrance]
- Despite what seems like common sense, you threw away the letter. [Drop Undyne's Letter]
- Undyne: Hey! Don't throw that away! Just deliver it! [Drop Undyne's Letter in Snowdin]
- Undyne: Oh my god! The letter's not to PAPYRUS!!!
Papyrus: YEAH, UNDYNE'S GOT A POINT! WHY DIDN'T SHE WRITE A LETTER TO ME INSTEAD?
Undyne: Fine, you want a letter!? I'll give you a letter!!! YOU GET AN "F"!
Papyrus: OH NO!!! WHAT'S THE F FOR?
[Examine Papyrus's mailbox with letter in inventory]
- The letter is too powerful to throw away. It gets the better of you. [Attempting to drop Undyne Letter EX]
If the protagonist spares Flowey after his battle in a no EXP earned Neutral Route, he tells the protagonist to backtrack and see Alphys. After reaching the bridge that connects the CORE and MTT Resort, Undyne calls the protagonist and tells them to come to Snowdin. In Snowdin, Undyne gives the letter to the protagonist.
If the protagonist defeats Flowey and has not befriended Undyne or Papyrus, Flowey instructs the protagonist to befriend the two characters. In this case, Undyne gives the protagonist the letter after they hang out. Befriending Undyne is only possible if the protagonist has gained no EXP.
When delivered to Alphys, she debates whether or not to read it before chastising herself, and opens it with some loud machine (possibly a chainsaw). At first, she believed the contents to be a joke being played on her and decides to confront the person who delivered it.
Alphys becomes flustered when she realizes that the protagonist is on the other side of the door; she believes that the protagonist wrote the letter since it was unsigned. She then goes on a date with the protagonist.
Undyne's letter cannot be sold in the Tem Shop. Its price is replaced with "NO!G," and if the protagonist attempts to sell it regardless, one of Mettaton's soundbytes play.