All Snowdin Easter Eggs Part 1 (pacifist run)

If you use a stick during battle

If you try to run away from puzzle.

If you try to run away from puzzle 2

If you use a stick against them.

You can find him in the cave if you walk for some time (think it's about a minute or 2)

Trying to enter before talking to Papyrus

If you call as soon as you get Papyrus's number.

If you call him again.

He got some from Shyren concert.

If you call him from his room later again.

If you call again.

If you talk to Papyrus before the end.