Back at Papyrus' house...

"Papyrus? Did ya check the best before on the seasoning?" Sans asked.
"Yes, I read everything on the packaging," Papyrus said nervously. What if he missed something? He walked into the living room.

10 minutes later...

WHOOMP!
"Sans? Did you hear that?" Papyrus asked.
"What, you mean that sound that sounds like a time machine that Undyne could hear from the Ruins? Yes, I'm pretty sure I did." Sans said.
Papyrus walked into the kitchen. "AAAGHHHHH!" Papyrus screamed as he got sucked in to the portal.
"Pap? You okay in there?" Sans shouted as he walked into the kitchen and got sucked in too.
Coincidently, they were put together as they were flying past other universes. They saw plenty of different games: Minecraft, COD: Black Ops III, Terraria and then finally got flung inside FNAF. They ended up in the office, where the night guard would be.