(Frisk's P.O.V.)

I'm watching TV with all the others when Sans comes downstairs. He looks awful.

'i'm going to grillby's,' he says.

'SANS, DON'T YOU THINK IT'S A BIT LATE. AND WE JUST HAD DINNER!' Papyrus yells to him.

'paps, please? anyway, i think we're out of ketchup. i could get some more there.'

'FINE. JUST DON'T BE BACK STUPIDLY LATE!'

'i can't promise anything,' Sans, replies as he walks out the front door.

'I'm going to the bathroom,' I say, standing. I leave the room but don't go into the bathroom. Instead, I slip outside and follow Sans.

You see, I've noticed that Sans only ever goes to Grillby's this late once a month and, when he comes back, he's in his worst state ever. Most of the time, he's limping and I swear I once saw he was covered in bruises and had a few cracked bones. It's definitely suspicious so I decided to follow him to see if he's hiding anything at the bar. And, if not, he may drunkenly say something to Grillby that will reveal the truth.

However, he doesn't head to Grillby's. Instead, he goes in the opposite direction. I continue following him of course, my suspicions growing. I finally see where he's going: Mt Ebott.

I have no idea why he's going there. The Underground's been abandoned ever since monsters came to the surface. As we climb, I look over at the sunset. It looks beautiful. I notice Sans is looking at it too. He, however, looks worried, scared even.

We enter the mountain and go through New Home. We walk all the way through Hotland and Waterfall. But...why didn't Sans just teleport?

We arrive in Snowdin. Sans looks around to make sure no one's following him so I hide behind Papyrus's old 'Capture Zone'. Sans doesn't see me and goes behind his house. I hear the door to his not-so-secret lab open, close and lock. I run around to the back of the house.

This is it, I think to myself as I stand outside. I'm finally going to find out the truth behind Sans.

I look through the key hole to see Sans...stripping?! Really, he takes off his hoodie, shirt, shorts, slippers and underwear. He gathers his clothes and puts them in one of the drawers. He sits on the floor, sighs and looks up. I follow his gaze to see something I never noticed the other times I'd been in there. There was a sun roof. Above that, there was a hole in the cave, showing the sky above.

'it'll be fine, sans,' Sans begins saying to himself. 'you've been through this so many times before. get yourself together.'

He's shaking. In fear? I mean, he's a skeleton. He can't get cold.

He looks back up at the sun roof and so do I. The clouds above move, revealing the full moon shining above. As moonlight pours into the lab, Sans lets out a blood curdling scream.

He falls forward onto the floor, face down, still yelling. I'm confused for a few seconds when I see it. His bone shifting and changing shape. His legs and arms are growing longer, his spine hunching. Claws push their way through the end of Sans's fingers and his teeth grow into sharp fangs. There's also...ears growing?! White, pointy, furry ears appearing on his skull. And he's growing a tail! His pupils go from white to bright yellow and his face starts stretching into a snout.

I...I don't know what's happening. I'm curious, worried and terrified. What I'm seeing is scarring. And Sans said he's been through this a lot of times. Why has he not told anyone about this? What even is 'this'?

Sans's...transformation?...finishes. He's a...beast. He stands up. I begin to wonder, is this even Sans anymore? Does he know who he is? Or does this creature have its own mind? If so, is it murderous? It looks like it, with those claws and fangs.

It...no, he. It's still technically Sans. Calling him 'it' would be making him seem like an object and not a living being.

Sans tilts his head up to the ceiling. He lets out a long, loud howl, kinda like a wolf.

Wait a minute...

Wolf, full moon, transformation...

I can't believe it.

Sans is a werewolf.