How di I get the Alphys and Undyne dating scene?

[Sour Grape Snape]

I know i have to get a letter, but i don't know when to get it.

[Russ Cabbage]

backtrack from the CORE to the bridge connecting it from the MTT Hotel, you should get a call from Undyne. If you don't, then go back and hang out with her and make sure you'd gone on the date with Papyrus. She should give you a letter to Alphys.

[MysticMalevolence]

After your first neutral run (per true reset, I believe), you get a call from Undyne on the bridge to the core after fighting Mettaton asking you to deliver the letter. Hilarity ensues if you drop this letter and return to Undyne.

[Submissive Succubbus Frisk]

Git gud

[Tim Timsen]

Originally posted by Gettin Down and Frisky:

Git gud

[Jamchow]

You shouldn't have spoiled yourself, then you'd know how to do it.

[Zeox]

Flirt, that's always the answer.

[Spectrum]

You have to do the following things:
1. Have 0 EXP.
2. Give Undyne a cup of water when she collapses.
3. Defeat Asgore and Flowey.
4. Hangout/Date with Papyrus. (can be done before #2 or after #3)
5. Hangout with Undyne. (can be done before or after #3)
Once you've done all of those, you should be able to get Undyne's Letter.