Many different monsters, such as many members of the Royal Guard, can be found relaxing, playing cards, and talking. When you accept to go with Sans when he goes to Grillby's on his break, it is revealed that Sans is a well-known regular, even having a tab.
Grillby's contains a couple of booths, tables, a bar and a broken jukebox. As mentioned above, it contains a variety of NPCs, from Big Mouth to Punk Hamster, including much of the Royal Guard, if the protagonist spares them before reaching Snowdin. The members of the Royal Guard that hang out in Grillby's include:
A full list of the monsters in Grillby's can be found here.
Neutral and True Pacifist Route
After sparing Papyrus and making it to the entrance of Waterfall, Sans will ask the protagonist if they want to go to Grillby's, as he is on one of his "legally-required breaks." If the protagonist agrees, he'll tell them to follow him, as he has a shortcut, and will proceed down the path the protagonist would take to proceed in Waterfall, which "transports" him and the protagonist to Grillby's.
Upon arrival, Sans is greeted warmly by the many patrons as he takes a seat alongside the protagonist at the bar, and asks the protagonist what they want, giving them the option of getting a burger or fries.
Now, while waiting for the protagonist's food to arrive, he begins to strike up a conversation, asking the protagonist whether they think Papyrus is cool. Grillby brings the protagonist and Sans the dish that the protagonist had chosen at the beginning of the discussion. Shortly after, Sans asks the protagonist if they are going to need the ketchup for their food. Once again prompting a choice by the protagonist, they can either choose "yes" or "no".
- If the protagonist says yes, they will take the ketchup and attempt to add some to their plate, but the cap falls off and ruins their food. Sans will then say the protagonist can have his food instead.
- If the protagonist says no, then Sans will say there's more for him, and proceeds to chug the entire bottle in one sitting.
Sans then goes on about how Papyrus had begged Undyne to allow him to join the Royal Guard, and the "training" he was receiving from Undyne.
Afterward, he tells the protagonist that "i wanted to ask you something." All action in the room seems to freeze. All light focuses on the protagonist and Sans, and "Premonition" begins to play in place of "sans.". Sans then goes on about how Papyrus had been getting advice, encouragement, and even predictions from a talking flower, but brushes it off as he felt it was simply an Echo Flower being used to play a trick on Papyrus.
Afterward, Sans will say that he needs to get back to his post, as the protagonist had "held him up" and asks if the protagonist is willing to pay the 10000g necessary for the meal, prompting yet another yes/no question. However, no matter the protagonist's response, Sans will say that he is just joking, and will tell Grillby to put it on his tab. He will then begin to leave, start a sentence but then forget what he was going to say.
If the protagonist kills Papyrus instead of sparing him, the monsters will complain that Sans is not showing up, and this scene will never take place.
The entire building is completely empty, as all of Snowdin had been evacuated at this point. Sans is nowhere to be seen.
- Papyrus states that Sans usually eats out every night, and only recently began attempting to cook. It can be assumed that Grillby's would be the "out to eat" that Papyrus was mentioning.
- There's a "fire exit" to the left of the bar, which cannot be reached unless the protagonist has killed Lesser Dog. However, the protagonist cannot use it as they are "not made of fire". This restriction implies that the exit was made for the owner, Grillby, only. This joke is a play on real life fire exits.
- Grillby is either mute, speaks a different language than other monsters, or is simply not talkative. This behavior is revealed after the True Pacifist Ending when the red bird, who usually speaks for Grillby, says "I might not get to translate for Grillby anymore..." However, Grillby says "................... good job."
- The presence of the dog characters around a table laden with cards, as well as Lesser Dog playing poker by itself, may be a reference to the Dogs Playing Poker series of paintings by C. M. Coolidge.