Wait.
What was happening?
The Little Knight had traveled this hallway before. they knew that. So how was it happening again?
They made their way down the hallway for the third time, making it to the pillar at the end. They were calmer now, they knew what would happen. The second time they went through this hallway, they had just gotten a strange sense of Deja Vu. The purple bricks stacking against the walls with cracks and wildlife overcoming them... The occasional pillars, some crumbling, some repaired. They had seen it before. But how?
They looked to Toriel, who made themselves known by sliding out of her hiding place. They looked to the mysterious phone, yet already knew what Toriel was about to say.
"Do not fear child, I did not truly leave you. This was merely a test. A test to see how you would handle yourself alone. And you did great..."
… But how? How had time somehow wound back?
"... There was a reason for this test. I need you to wait here, I need to go do something. Please don't go on by yourself... It's dangerous. Do you understand?"
They nodded, and Toriel left the room. Then they started pacing.
So, they had walked through this hallway with their nail out. They knew that. Then, they waited in here for Toriel, just like she had asked. Then, they had heard their phone ring. When they had picked it up...
All they could hear on the other side was a beast's viscous snarling.
They had ran out of the room, nail drawn, unaware of the spike puzzle, and had run straight onto it. They had never found Toriel, as they had bled out on those spikes...
So how were they alive? What happened?
It didn't matter. They were determined to find Toriel.
They didn't wait this time, they rushed right on forwards. This time, however, they flipped the marked levers before. Yeah, surprising that spikes would make them bleed.
They would slash through any who tried to stop them.

"What the hell is that thing."
Chara said as they stared at the big... thing... blocking them from going to this new grassy area. There had been a sign, though they didn't care to read it. Besides, they didn't know how to read it anyways. Maybe it was a sign warning them about this ACID SPITTING MONSTER-
Frisk quickly got out of the way, just for them to spit another monster at her. They were a tiny rolling thing, like a Pill bug. Except they hurt. A lot.
Frisk slashed it down, beating it dead, then attempted to slash through the big guy.
Clink!
The large monster blocked her by curling up. It's thick shell stopped her from breaking through, and it didn't attack. It was hiding. Coward.
They walked away, letting them come out of their shell. Then, they ran as fast as they could forwards, and slashed again.
Clink!
Clink!
Clink!
They weren't getting anywhere.
Sighing, Frisk gave up, running away from this seemingly undefeatable foe. She would come back later.
For now, they went back to the big room with the broken chandelier, and went down. That was the only way they hadn't explored yet.
As they approached, however, they heard a being. Someone alive. Thank the gods.
They entered the room to find a large bug. They were wearing tiny glasses, and a nose that trailed all the way to the floor. They had paper all over the floor, and seemed to be drawing? No, mapping. They were mapping.
Score!
They went to them, and learned that their name was Cornifer. Cornifer the Cartographer. That reminded them of someone...
Sans the Skeleton
Cornifer the Cartographer.
... Even here, their sins would crawl down their back.
"... Frisk?"
After getting the map, Frisk turned away. They went through the ruined Crossroads. They must have been nice once, a place for monsters to travel between different areas of "Hallownest". Now cracks ran deep through the stone, and it was rare to see a place that wasn't falling apart at the seams. They traveled forwards, learning different things about Hallownest as they traveled. Slashing downwards on an enemy launched them up, and they could continue doing that while staying safe. They also learned about Aspids- And to avoid them. The water was acid most of the time, and apparently the orange stuff is called "infection", and drove everyone insane.
Good to know!
They sighed as they came to a sign. Another unreadable object, though it looked like some sort of horse thing? They followed it upwards to an odd building, a bit less worn than the others. They went inside, found a thing to pay for... something. So she paid, and it sank into the ground. Up came a bell!
They decided to leave it be, resting a moment on the bench, then going forwards. A certain doorway caught their attention. It was a bit paler than usual, and it also had strange carvings and- surprise surprise!- cracked pillars barely keeping it up. A strange doorway, what could go wrong with entering?