Mono stuck close to Frisk when they traveled to the hotel. She asked if there was any other way out, but no. Apparently Frisk already went to the hotel, found out the elevator was broken, and tried to look for a way to fix it. As it stands, going through the Core was inevitable. The pup wished that the underworld wasn't so linear. When they reached the entrance to the Core, the kid must have caught her trembling because she pet her head to comfort her.

"Just stay close, It'll be fine. The elevator will takes us through it." they said.

Mono was not reassured.

Mono's assumptions reigned true because while the human thought they were being productive, the elevator was not working when they arrived.

"I don't get it, Alphys said it was fixed."

"It doesn't look fixed to me. I knew we couldn't trust her!" said Flowey.

"I'm going to give her a call." Frisk said as they pulled out their cellphone.

There was a moment of silence as Frisk dialed Alphys and talked to her.

"The elevator is still off. Huh? Okay, hold on." the human stopped talking for a moment to walk through the door on the right, only to come back out a few seconds later. "It's a dead end. No, it's fine. Thanks for trying to help us! Bye."

"Well?" asked Flowey.

"Alphys's ability to manage the core from her lab is being overridden. She can't help us in here."

"Looks like dingbats wants us to walk." Flowey replied with an annoyed tone.

"It's WingDings." Frisk chided

"Whatever."

"What? Nonono we are not walking." Mono argued. "The doctor's in there and I kind of enjoy being not dead."

"I know you're scared of him, and so am I, but it's the only way out. We don't have any choice but to walk through his trap."

"Fine..."

After heading down the left hallway, the team was met with a long bridge guarded by lasers. Frisk said that blue meant stop while orange meant go, but that only helped so much when the lasers activated in random orders.

The Core was very bright; or at least the main chamber was. Everything below the walkways seemed to get swallowed up by a white glow. Frisk urged the pup to be careful not to fall. The human seemed to know exactly what they were doing and where they were going; including solving the gate puzzle and navigating the maze-like core with ease. To Mono, everything looked pretty much the same, so she was glad that she had a guide.

Soon they all crossed the long bridge and were met with another doorway with an elevator next to it, which was still out of order. Frisk walked over to the wall and appeared to touch something in the air before going back to the doorway. Mono stayed close behind as they walked into the dark room up ahead

Inside of the room was a figure that the pup found very familiar. He was a skeleton, around Papyrus's height, with the same outfit that Alphys wore back at the lab. A scientist.

"I see that you've found my subjects. I've been waiting, and I'll even let you pass freely if you give them to me." he said.

"Gaster, you can't have her. She's going back with me. This world is corrupted and you know it!" said Frisk.

"I was being negotiable, but it seems like you want things done the hard way. This world is corrupt because of your own doing, now suddenly you want to fix things? I actually plan to help all of monsterkind."

"By killing her? Why would that help anyone?"

"Because, child," He pointed to the scared wolf pup hiding behind Frisk, "What you have behind you is a milestone in science. The first successful subjects of soul splicing; the act of removing souls and merging them into one."