Papyrus: Fast attacks and combos, ranged and melee, but isn't the most mobile.



Sans: Fragile and low-damage, but very mobile, with teleportation out the coccyx. Karmic Retribution is present, but only if he lands a direct hit.



Muffet: lots of command grabs, I imagine. Can regain a little health by eating spider confections.



Undyne: Lots of hard-hitting attacks, but cannot block and is very slow. Can immobilize opponent to make the initial hit of a combo easier to land. Lots of melee.



Mettaton EX: Strong, fast, and active, but super heavy and slow to get up after being knocked down. Mostly melee, because LEGS!~



Asgore: Relies mostly on sweeping, heavy hits with his trident, and slow, but consistent combo damage. Cannot move very fast, but has the fifth-highest DPS, below Frisk, Chara, Asriel, and Gaster, in that order.



Toriel: Ranged fire attacks and melee counters that put distance between you and them. Average stats all around.



Alphys: Uses lasers and Mini-Mettas, can summon some of the Amalgamates to attack for her by throwing Popato Chisps.



Lesser Dog: Melee, can extend his head for attacks. Gets pet when grabbed, briefly stunning him.



Napstablook: takes very little damage 'cuz he's a ghost. Tear attacks work best at medium ranges. Can throw grey attacks to disrupt your opponent's blocking, and follow up with regular attacks.



Frisk: Attacks with the weapons of the fallen Humans, is a little fragile, but has the fourth highest DPS in the game.



Asriel: This is Asriel in the first stage of his boss battle, fighting with Chaos Sabres, his Chaos Buster, Shocker Breaker, and Star Blazing, all of which he announces like a weeb. They all deal massive damage, even more than Chara and Frisk, but are easy to see coming, so blocking or dodging is key, but you've got to memorize it.



Chara: Uses the Real Knife to deal crazy damage with simple slashes that send the opponent sprawling. Does extra damage to monsters. Can paralyze enemies with her Scary Face.



Temmie: High-risk, high-reward attacks, with are strong and fast, but take a second to recover from. Temmie can actually go toe-to-toe with anyone, played properly. Can spray Temmie flakes. A surprised face lags behind her when she dodges.



Madjick: fast, ranged attacks that can stun and alter the opponent. Like Asriel, announces his attacks with magic words.



Doggo: Good at interrupting opponent, can pounce on the enemy and deals extra damage if the first hit interrupts their attack.



W.D. Gaster: uses Gaster Blasters and copies of his hands, as well as opening gateways to the void to keep the opponent pinned. Long-range combos that can chain off and have the opponent on an assembly line to destruction. All of his attacks are tremendously damaging, more than anyone else, but get within close range and stay there, and you can easily thrash him.



Special skins include (but are not limited to) Genocide, AUs (UnderFell, UnderSwap, UnderFresh, EpicTale etc.), Possessed Frisk , Flowey, Scientist (Gaster and Sans), Lost Souls, and Human Souls.