Get dunked on, Bro

First off, Mario has shown to be killed quite easily. He can be tapped by a turtle and would keel over. A maximum of 3 touches in the standard platforming games should he have the most power ups he can have at once, excluding the star and mega mushroom.

Second, Sans is a serious “don’t judge a book” character. While he has 1 Attack, Defence and HP, he is one of the hardest bosses in the game if not the. Be it his teleportation, his blue attacks (alters gravity), summoning bones or even Gaster Blasters, he has a very large arsenal and a pattern that only can be figured out after many fights, making him far worse than Bowser.

Third. MagicalKeyPizzaDan was to compare how Sans was taken down by a kid with a knife. Frisk (or whatever the player calls him/her) was able to take down some of the strongest beings in the underground, including Undyne. Undyne was able to shake her whole house with a stomp, is able to suplex large boulders and was so determined that she was able to regenerate! Getting back to Sans, he was able to beat Chara many times. Spoilers, but Chara is a spirit that guides the protagonist down the Genocide Route and  (upon completion of said run) wipes out all of reality after killing Frisk!

There is one last thing: you may be asking (if you haven’t played Undertale) “if Sans has only 1 attack, how is he so freaking strong?” (the protagonist at LV 20 having 99 HP 48 Attack and 14 Defence for reference) Well, Sans has one last trick up his sleeve: Karma. His “Karmic Retribution” acts as a poison and is proportionate to the EXP of the player. Another tidbit, EXP and LV/LOVE in Undertale mean Execution Points and Level of Violence. The reason Frisk was so vulnerable to Sans’ attacks was because of all the death he/she caused while in the Underground. Here’s where it gets fun, kids! If we take the first level of New Super Mario Bros for the DS as a base and assuming there are the same number of enemies in world 1-1 (17) as there are in the other levels (*79) and the other platformer games in the SMB series (*15) discounting bosses and games that don't fit the norm, Mario can kill a rough 20145 enemies in all normal platforming games. That’s not the half of it, in the original Super Mario Bros manual, the citizens of the mushroom kingdom were turned into blocks. Adding that into our little mathematical formula (17+75) brings it up to a whopping 109020! This means under the rules of the Karmic Retribution, Mario is thousands of times worse than Frisk can ever be! That’s not counting the bosses, Yoshis and so on.

Where does Luigi fit into all this? Well, his somewhat cowardly and not as big a monster as Mario (though he had a game where he did the same), he’s likely flee when he feels his sins crawling down his back.

Clearly I have too much time on my hands.