His motivations are to capture a human so that he can become an official member of the Royal Guard, a very prestigious job.
He has a dream of seeing a human. A disadvantage of his is that he is almost as weak as Canon Sans, leading to being denied a position in the Royal Guard. However, he is very cheerful and much more energetic than UnderTale Sans. He is very positive and enjoys making tacos for his friends.
He also can open his mouth.
His stats are similar to Canon Papyrus', being 20 HP, 20 ATK, and 20 DEF, but this in some (Maybe hard to find) versions, he has the same starts as classic Sans but different role.
UnderSwap Sans is similar to Canon Papyrus in a lot of ways, but there are also some differences! For example, instead of "NYEH HEH HEH!" or "WOWIE!", UnderSwap Sans will say "MWEH HEH HEH!" or "WOWZERS!" UnderSwap Sans has a liking for riddles rather than puzzles, and still enjoys puns. He also collects Sci-Fi figures instead of action figures. 
He is often referred to as "Blueberry" by Fans because most of them find him cute, along with the fact that most of his clothing is blue. However, Blueberry is a Fanon rendition of UnderSwap Sans. He appears to be more cute, innocent, and sometimes more baby-like, unlike the original UnderSwap Sans. Blueberry is not canon to UnderSwap and is not the correct portrayal of UnderSwap Sans.
He is NOT a Yandere. (Unless you're looking for YandereSwap, if you want Yandere Blueberry then look at that, classic Blueberry isn't though.) He is only put as a yandere in some memes and dubs for reasons of his love for Red or Dust, which is a common ship and this version of UnderSwap Sans brought to life.
His arms are by his sides, and he appears standing up straight and still, facing the player like UnderTale Sans. He wears a slightly tattered blue cape that appears to be
a bandana of some kind, although it could just be how it looks. The bandana appears to have a small hole close to the bottom. He wears a gray sleeveless shirt with a white t-shirt underneath, along with gray shoulder pads with baby blue outlining. He wears pants with a slightly faded blue look to them, and he wears blue boots that match the color of his cape. His shirt also has half-circle shaped pauldrons.
In Battle Appearance
He stands in the same position as UnderTale Papyrus but is much shorter. Aside from his dimpled smile, (which is similar to, or if not exactly like UnderTale Sans'), his facial expression is mostly like UnderTale Papyrus'.)
When Sans first met Chara, [In this AU, Chara would act like Canon Frisk] he immediately wanted to be friends with them. He is very happy to have Chara as a friend, but disappointed because he cannot join the Royal Guard for befriending Chara, who is a human.
Sans and Alphys are best friends. Sans wants to join the Royal Guard, but Alphys secretly will not let him since she cares about Sans and refuses to see him get hurt because his stats are too weak in battle. They hang out all the time. Alphys is also the one who is training him.
Sans starts a Temmie fan club, as told by Temmie themselves in the Neutral Route. It is known that Temmie doesn't like Sans, but it is unknown what Sans thinks of Temmie.
Sans and Queen Toriel are confirmed to be best friends, just like Undertale Sans.
Sans and Asgore are friends.
Non-Canon (Fan-Made) Theme Songs
(The intended theme for UnderSwap Sans would be one with a "Song That Might Play When You Fight Sans" leitmotif, therefore making Mweh Heh Heh! + BoneQuarrel, and Passive Megalovania non-canon to UnderSwap.)
- Even though he does get annoyed when Papyrus tells puns, he doesn't hate them.
- He also appeared in the Christmas Party AU comic.
- He was also the one who spiked the eggnog at the Christmas Party.
- there is also a Blueberror version of himself.
- The creator has admitted that they didn't like like that the AU Community referred Swap Sans as "Blueberry", which is part of the reason why they decided to cancel the AU.
- Another reason why the creator cancelled Underswap is because of Fontcest.