Fell WOULD have won at that final attack, but the human apparently pulled a pie out of their place that the sun don't shine and healed back up to max. *Twice.*
I have a headcanon that 1 hp makes his soul/magic not weak, but unstable. such an intense battle will leave him in a very weakened and unprofitable (if not near-death) state. the waste of magic does not pass without a trace, which is why he is so exhausted in the process. and if undertale sans does not like to fight because of moral beliefs or laziness or something, then underfell sans (who 𝙧𝙚𝙖𝙡𝙡𝙮 needs it for self-defense) doesn't want to put a target on himself. like, they'll just pounce on him en masse and take him in quantity or catch him when he's already exhausted. his power will make his head a trophy.
I believe the stronger the body the weaker the Magix example undyne she is a unit Stat wise but can barely produce advanced magic patterns while sans has literally 1 attack and defense but can literally poison you and do attacks no other monster can
What's funny is that Canonically, Underfell Papyrus *SHOULD* know Underfell Sans is pretty strong after witnessing an angered Sans almost try attacking Underfell Asgore. He also should know *WHY* Underfell Sans doesn't really fight so I mean...
Something interesting that I realized is that Fell! Sans is actually a bit underpowered (damage wise) compared to Classic Sans in this fight. Let me explain, their KR scaling. Classic, for example: for each 1 damage dealt by his bones, the human takes 6 additional damage to KR, making even the slightest hits devastating in sticky situations. Fell, however, doesn't have this much KR damage, at least not here, instead, for every 1 damage, there's around an additional 1 KR damage. Basically, what I'm saying is, that if Fell had the same KR power as Classic, his fight would be devastatingly difficult, and we're lucky he doesn't have Classic's KR.
Bro, just one tip. Make Sans and Papyrus have no hair, if then it's PERFECT. (sans and papyrus having hair = offense) Undyne is pretty average. Alphys is 100% canon, good job.
underfell canon and fanon designs aren't that different but I don't like underfell fanon I have seen enough of it to have a reason not to like it if I'm being honest not just underfell fanon but underswap fanon and ut fanon? that's much worse I see people making sans depressed, way too serious, I'm not going to add another cause it won't be a good one...
man you gotta credit me and traxsus for making these games and akt for the videos you used like you're lucky im even letting this shit stay on this platform