Edited
...Calaca Vs
Yes, Sans can be considered a glasscannon. But only considered one when facing Human Opponents. Or Opponents that has a high level of violence. So... In a monster's perspective(Ones within the underground), which are mostly creatures not attune to violence, Sans can be considered as one very weak monster with stats of 1. Which he states when he fought Chara in the Last Corridor. Also, Sans is a Genius Tactician and Scientist. We don't even know where he got those experiences from but he has them as well as some experience with battle as seen when fighting Chara. Undyne on the other hand, can be considered as the 2nd strongest monster within the underground with her being below and trained by Asgore himself whe she was young. She also fought her way to get her position(not like there's a lot of Monsters willing to take such position) but nonetheless it shows how strong she is compared to other monsters. Though fighting is really all she's probably good at(burned her house while cooking), she has a good sense of danger and reaction time considering who trained her. Though her LV would probably be high(maybe higher than 20 or lower, we don't actually know the base stats of monsters and their growth, not like it matters within the game) she has the instincts and strength to use it which she trained and strenghtened for a very long time. She also have high resistance to a lot of manipulation like Soul Manipulation and Fire. Comparing her to Chara, which has her levels going up in a short time and not being able to hone skills with it. It's like comparing a Serial Killer to a Proffesional Hitman. But considering Chara has timetravel hax which makes her go back to a certain time each death......yeah... we have a timetraveling Serial Killer. Anyways... I'll add some stuff later... gonna read up to things.
Added
==
Side Note: So... I don't know how KARMA works or if we can even use it in this one but I'll just add it cuz it's there in
Sans Vs Page. ... Nah... More like, let's consider the things listed in both their Vs Page.
==
Reply: xD
==
Anyways, as how things look or as I probably just listed up. Undyne can be seen as the winner as she got: Regenerationn(just saw that in her vs page and forgot to add. Then again I don't know if it actually means Regenerationn=Regenerationn or Regenerationn from Determination), Better Resistance to Soul Manipulation than Sans(He only has Minor Resistance), Is the 2nd strongest monster within the underground(also 2nd strongest enemy in Genocide route that is without the hax as other monsters have except for Determination) and has better experience in fights as she was trained by Asgore when she was young. In her Undying mode, she also gained Determination, something we don't have much information on but means to persist death in the
Undertale Wiki,the only thing that kept her from fading, and increased stats of a lvl 20 Chara.
While Sans... 1 point stats, Genius Tactician & Scientist, Gaster Blaster, Bones, Weakest monster... and Knowledge of Alternate Timelines... Yep, I got no basis on this except for the info from the His Vs Page and my own thoughts, since looking at it from this angle it's very unfair for Sans the Weakest Monster in the Underground to be facing against Undyne the Undying, the Genocide boss stronger than Asgore. I could actually just put Sans KARMA attacks into this one, but after reading what Karma means and what others think of what KARMA means in the game... I've decided against it as it would probably do no more than 1 extra damage unto Undyne(I dunno maybe some Petty Karma Consideration). So then I thought and looked at both pages(not too much cuz I think I'm missing something here) and then focused on Sans having knowledge of Alternate Timelines. No, I'm not talking about the other Au's like Underfell, DustTale or anything... that'll just be... Anyways, I'm talking about the alternate timelines within the Undertale game. Timelines where there's a Pacifist Ending, Neutral Ending and Genocide Ending. Cuz really, ever wonder as to why Sans, the weakest monster within the Underground became good at combat? I mean, yeah, it might be a bit farfetched but he was able to fight and/or stall Chara for a very long time and make her do the process over and over again, though KARMA might've been one of the reason this comes to play not that it matters much as he was able to last quite longer than monsters more stronger than him(but still die just as quick i.e. single slash), this shows that Sans probably gained or learned things within those timelines adding them into his attacks and strategy making him more better in combat. Not only that but I think this also add up on different Genocide Routes in Different Timelines which makes him able to evade attacks made by Chara(I'll talk more about this theory if someone actually opens one or gives me a link to one already existing. Or just give me a link to one that's already closed. I'd like to read more on that). In the end, this doesn't actually gives him much fire power against Undyne as all it gives him is some more tricks he could use against her... that's all.
I can't actually think of a way for Sans to win against Undyne in a Monster vs Monster battle as he, like I've said is Considered the Weakest Monster in the Underground. Although knowledge from alternate timelines would give him a better chance towards other monsters even Normal Undyne but against Undyne the Undying? Yeah... I don't think this'll work out at all.
So yeah... as much as I love Sans... I'm voting Undyne.
=
Reply:
Not debunking you but if you want me to try just tell me. And give me a few days.
=