Papyrus

Papyrus is one of the main characters in Undertale.

The player is first introduced to Papyrus soon after meeting Sans outside of the Ruins, wherein Sans says they are brothers. How the rest of the encounter, and the player's interactions with Papyrus throughout the game, plays out is affected by the route the player is taking.

In the Genocide route, despite the player not responding to Sans telling them to hide behind the lamp, Papyrus doesn't even acknowledge them standing out in the open as Sans states that he has indeed seen a human, leaving just as quickly as he came. Later on, the player will meet Papyrus again past the Box Road where he's initially talking with Sans about when the human is going to appear. When Sans suggests that he look in the direction your just coming from, Papyrus initially thinks he's talking about the rock behind the player and still doesn't know who, or what, the player is until Sans helps him use the process of elimination. Papyrus will then warn the player, in the playful manner, that they will face many puzzles and risk being captured if they proceed any further. When the player reaches the Invisible Wall Maze puzzle, Papyrus will attempt to explain how it works only for the player to just walk up to him through the puzzle area before it can be activated. Past that area, the player will run into Papyrus and Sans again with "obstacle" of a cross-word puzzle before them. Ignoring the puzzle, Papyrus will point out that it did nothing and Sans will comment that he should have gone with a "Junior Jumble" puzzle instead, which is Papyrus' favorite. Further along, the player will come across several more of Papyrus' puzzles but they will be unactivated. When the player reaches the Colored Tile Puzzle, Papyrus will attempt to explain the puzzle only for the player to once again just walk through it before it can be activated. After talking with Sans, Papyrus will ask the player a question, but they won't respond. To this, Papyrus decides to leave the instructions for the puzzle for the player to look at and do it themselves. When the player reaches the bridge to Snowdin, Papyrus will prepare a more deadly trap for you but will decide not to activate it since the player just walked through all of his puzzles. Finally, when the player is about to leave Snowdin for the Waterfall area, Papyrus will confront them about their behavior including how they walk around with "powder" on their hands. Unaware of what the player has been doing, Papyrus will believe that they are simply starting to lose their way and will offer to be friends so that they will stay on the "straight and narrow." But even after the player kills him, Papyrus will still believe that they can be a good person.

In the Genocide route, if the player spares Papyrus then they won't have to battle Sans at the end. Likewise, if the player takes the Neutral route and kills Papyrus, they won't have to battle Sans but he will make his anger about it clear.

In the Pacifist route, the player will listen to Sans and hide behind the lamp just before Papyrus arrives. Sans will greet Papyrus casually but he'll come straight to the point that Sans hasn't recalibrated his puzzles for days. With Sans' successful use of reverse psychology, Papyrus will ignore the player's hiding place and instead go on about how someone as great as himself will soon get all the things he "deserves" while Sans will never amount to anything. Once Sans starts telling his jokes, Papyrus will storm off saying he has to see to his puzzles. When the player comes out of hiding and is about to leave the area, Sans will ask them to actually show themselves the next time they meet Papyrus, saying that he's been feeling down lately and might cheer up from actually seeing a human. Sans will then assure that Papyrus isn't actually dangerous, "even when he tries to be."

Past the Box Road, Papyrus will be seen talking with Sans and will about to say something about Undyne when they notice the player's approach. Papyrus immediately thinks he has finally found a human, only for Sans to point out that he is actually looking at a rock in the road. Once Sans points out the player in front of the rock, Papyrus will be overjoyed at the prospect of finally getting recognition for his "greatness." He will then proceed to "threaten" the player not to proceed any further before leaving, presumably to prepare his puzzles. Reaching the Invisible Wall Maze puzzle, the player will finding Papyrus accusing Sans of being lazy because he was "napping" all night and referring to Sans calling that "sleeping" as an excuse. Noticing the player, Papyrus will go on to explain how the puzzle works with the player staying in place to listen. The way the puzzle works is that should one touch the invisible walls of the maze a blue orb will unleash a powerful jolt of electricity, but when the player goes to move through the maze Papyrus is the one who gets electrocuted. With Sans suggesting that the player should be the one holding the orb for it to work, Papyrus goes to hand over the orb to you, leaving a distinct trail of footprints showing the way through the maze. Should the player make it through the maze without getting electrocuted, Papyrus will express genuine astonishment at how easily you "solved" the puzzle, only to warn that the next puzzle won't be as easy since it was designed by Sans. Speaking with Sans before moving on from here will reveal that Papyrus' outfit was initially made for a costume party a few weeks earlier, and he thought it was so cool that he hasn't worn anything else since calling it his "battle body."

Arriving at Sans' "puzzle", Papyrus will just start to announce the puzzle only to ask Sans where it was as he didn't see anything noteworthy. The "puzzle" in question is a children's word search left on the ground, and regardless of whether or not the player actually looks at it or not, Papyrus will quickly point out that it did nothing to stop you. Hearing from Sans that it was a word search, Papyrus will get into a slight argument with him about word scramble puzzles being harder and will ask for the player to settle their "dispute." Talking with Sans before leaving this area will reveal that, the day before, Papyrus got stumped trying to "solve" the horoscope. Right away the player will run into another of Papyrus' traps, which is a plate of spaghetti meant to be so delicious that the player cannot progress. However, the spaghetti is so cold that it froze to the table and the nearby microwave is unplugged, so the player can progress without incident.

After the Dogamy and Dogaressa boss fight, the player will find a series of puzzles set up by Papyrus who has actually gotten himself stuck in place by them and is struggling to solve them again. There are some signs that give hints on what to do for the puzzles, and Papyrus himself is willing to give you hints should you speak with him.