Papyrus was already upset from the death of his own brother, but Undyne's own death was enough to spark him with a powerful rage he never felt before. He knew what he had to do. He had to put an end to the menace who had done this all. His eye glowed a bright orange, comparable to the one responsible for the murders of his friends.
Before Papyrus stood a fuzzy, orange creature. This creature had two fuzzy ears on the top of his head, and eyelids hanging down like he just got out of bed. This was no monster. It had a bustin' dialect. He's a cat, and Papyrus knew that. He's fat and he's lazy, he sleeps and he's so crazy. He reminded Papyrus of his own brother. This is mostly why Papyrus didn't want to kill the cat.
This cat was Garfield Arbuckle, a cat who hated Mondays and loved lasagna. Garfield most likely would have spared monsterkind from his wrath, had the day not specifically been a Monday. Before Garfield stood a zany skeleton man, who he had met back in Snowdin. The skeleton's zany actions reminded him all too much of the likes of Odie and Nermal. This is exactly why Garfield wanted so badly to put an end to the skeleton.
"CAT, I AM SO SORRY," said Papyrus, "EVEN THOUGH YOU DID SO MANY BAD THINGS… I PROMISED MYSELF TO ALWAYS FORGIVE. EVERYONE DESERVES A SECOND CHANCE… THAT INCLUDED SANS."
Papyrus no longer believed in Garfield. Garfield tried swinging his weapon, a trusty newspaper, at Papyrus. However, Papyrus used his worn bone to block the attack. Papyrus then responded with a flurry of Gaster Blasters. Due to Garfield's fat, the attack barely did anything. However, Garfield was then attacked by a storm of orange and cyan bones. Garfield followed their directions lazily, yet still managed to escape them unscathed.
"I DON'T WANT TO HURT YOU," stated Papyrus, "I JUST WANT TO TEACH YOU A LESSON."
Garfield knew their was a change in this skeleton's behaviour. He used to be zany, but now he was much too serious. And on top of that, he was extremely aggressive now. But Garfield didn't have much time to think before Papyrus began to fire more attacks at him. Bones and blasts flew all over the judgement hall, with Garfield barely taking any damage from direct hits.
"I know this isn't what you normally act like, so what's the deal?" asked Garfield, "Shouldn't you be acting all zany and eating spaghetti and stuff?"
"BUT YOU KILLED MY BROTHER," said Papyrus, "AND UNDYNE, AND METTATON, AND-"
"So? Shouldn't you act like yourself while doing this?" Garfield asked. Hopefully the skeleton wouldn't catch on to Garfield's plan of making his opponent soften up.
"...I THINK YOU'RE RIGHT." declared Papyrus. The orange glow faded from his eyes, and the worn bone disappeared. "I'LL DEFEAT YOU WHILE STILL BEING MYSELF! NYEH HEH HEH! TIME TO DO THIS MY WAY!"
Garfield's plan had worked, he really was dealing with a true bonehead. However, Garfield didn't have much time to think before Papyrus began firing bone attacks at him. This attacks were different, less focused and more energetic. The bones were bouncing all over the place instead of being aimed directly at Garfield. The bone attacks themselves were also fairly zany. There was a bone wearing a "COOL DUDE" t-shirt while riding a skateboard, and also bones spelling out the words "COOL" and "DUDE".
However, Garfield then saw Papyrus' most amazing feat yet: a large mob of bones in front of him, with an enormous bone behind the smaller bones. Garfield managed to jump over the smaller bones, but the larger bone was simply too tall. Garfield gripped onto it with his claws and began climbing up. "I think I'll put that skeleton's lights out." thought Garfield upon reaching the top.
Garfield grabbed onto the top of the bone and picked it up. Papyrus was in sheer amazement by this feat. Garfield then jumped behind Garfield and swung the bone with all his might. This was powerful enough to smash Papyrus into dust right away.
"Man, I really hate Mondays." Garfield thought aloud.
Meanwhile, in the Gateway to Heaven.
Papyrus' spirit had quickly appeared near the gateway to Heaven. Papyrus' was certain that all of his acts of heroism would allow him entry. Papyrus skipped to the end of the line. The line was mostly composed of other monsters that Garfield had slain.
After three days, Papyrus was in fifth place of the line, just close enough to see others in line being judged. The first person Papyrus saw being judged was a skinny cat who had accidentally stumbled into a volcano. The cat stated that it had spent it's entire life beating up dogs before it found itself burning in magma. The cat was allowed through the gate into Heaven.
The second person Papyrus saw being judged was a Final Froggit. Before the Froggit could even testify to the judge, a trapdoor underneath it was released, sending it straight to Hell. Papyrus was confused by this.
The next two in line, a Knight-Knight and a Astigmatism were also treated the same. This was a puzzle to Papyrus, but he stepped up to be judged himself. He looked up and the judge and everything made sense to him.
The judge looked exactly like Garfield.
Before Papyrus could even speak up, the judge pulled a lever which sent Papyrus careening down into Hell. Upon landing in Hell, Papyrus saw that he was surrounded by pale yellow dogs with giant, drooling tongues. Before Papyrus could react, the dogs began biting down on his bones and separating him into pieces.