Sans wears the usual blue hoodie and pink slippers. However, when his depression hits him hard he opts to wear an oversized red hoodie and navy blue slippers because they better fit his mood. When his sleeves are rolled up (which is a rarity), the many scratches, cuts, etc. are visible on his arms. They are also shown to be on his ribs and thighs.
Sans' personality is mostly the same as Undertale Sans'. He still tells puns religiously and is incredibly lazy, but now he has open fits of depression and occasional suicidal tendencies. They usually start after he's fought with Gaster, when he's done too much thinking by himself, or after he has too much ketchup. Sans is often neglected; this leaves him wishing Papyrus either wasn't the way he was, or wishing he wasn't around at all.
Sans loves Papyrus with all of his heart and wants to be a good big brother, but also holds much resentment for him. Since Papyrus is the favored son, he gets all of the positive attention that Gaster has, which leaves Sans in the way of the bad mojo. This further ruins his feelings for Papyrus, and on some occasions he may lash out at said brother (though will always apologize immediately after).
Sans and Gaster's relationship is not the best, even though the two try to make amends on occasions.
Sans has some beef with Lucario and does whatever he can to keep him away from Papyrus and Blue. For whatever reason, the two butt heads and, if left alone for long enough, Sans may try to attack Lucario.