Sans is the brother of Papyrus and the snowdin sentry. He first appears in the Snowdin Forest.
He still wears the same clothing, but it's more dirty from blood. His eye always glows red. He's got big cracked hole in his head. Sometimes he's portrayed carrying a big axe, but in the original comic Sans isn't seen carrying any weapon (Expect one mini-comic, where is Sans seen carrying a bear trap), he is also very scary because he kills for fun.
Sans looks pretty much bored with everything. He seems to be perfectly fine with killing and eating humans, however he appears to avoid eating humans himself. Even going so far as to have notes to Papyrus stating to stop him if he ever tries to eat anything moving (humans, he outright specifies). He also hints in previous pages of the comic at his avoidance of human meat. Like the original sans, he cares for his brother deeply & still sleeps at his sentry station. He also enjoys making head dogs (hot dogs made from severed heads), and cruel pranks. He is known to enjoy more psychological torture, which is why Flowey warns Aliza of his traps.
Sans made his first appearance in the Horrortale mini-comic Sans creepy advice, where Aliza decides between Sans's head dog and Papyrus' spaghetti.
Then he appeared in one panel of the mini-comic Fresh HotDogs and Everlasting love. In the third mini-comic Date with Sans, he and Aliza stare at each other for 10 minutes, then Aliza decides flirts with him to break the ice between them. Sans then bursts in laughter & continues with anormal conversation.
Sans makes his first appearance at the Ruins, where he killed Aliza with his bone attacks, after Toriel gave him a signal. When Aliza becomes alive again, he attackes once more, but in this turn, Toriel protects her.
When he appears in the forest and scared Aliza, he soon gave her a hand with a spinning spike attached to it. He was holding onto Aliza's hand for a while, until he finally stopped. Then he told her that Papyrus wants to capture her, and told her to hide behind a corpse. When Papyrus came, he told him where Aliza was hiding. After the second puzzle (the orb and bear trap), Sans tries to tear Aliza's ear off, because he realizes that she can save & reload, Sans first thought of it as cheating. He disappears when he hears growling from the woods.
He is seen again offering Aliza his Head dog. She accepted Papyrus's spaghetti instead. Sans then scares her by telling Aliza that Papyrus' spaghetti was made of the past human children that had fallen before her.
We don't see him again, until we reach a scene where he teleports Aliza away from Grillby's. she is half-cooked, and Sans says that he hasn't eaten a human in ages (7 years), so he holds himself back from eating Aliza alive.
Aliza - Sans doesn't really care about capturing humans. But he likes hurting them for fun. His gore puns make Aliza really uncomfortable. Beyond this, Sans tried his best to resist the urge to eat half-cooked Aliza, and he also teleported her from death, so he might care.
Toriel - It seems like they are still in contact. He was the one who told her how terrible the world outside the Ruins is at the moment, which seriously damaged her sanity. He also tried to prevent Aliza from escaping the Ruins.
Undyne - Sans hates her. He calls her queen Undick, and in the game, he said:"Personally, I kinda want her dead. But then, who'd be left to rule this paradise?" It was confirmed, that she was the one who broke his skull because he wasn't following her orders.
Papyrus - Their relationship is pretty much the same. Sans convinced him to eat the humans, so he won't die from starvation.