My last 10 games (and lead characters) are:
Man of Medan- the passengers of the Duke
Genshin Impact- The Traveler
Ni No Kuni: Wrath of the White Witch- Oliver
Fall Guys- Beans
Among Us- Crewmate
Dark Cloud 2- Maximilian and Monica
Death Stranding- Sam Porter Bridges
Kingdom Hearts Dark Road- Xehanort
Cuphead- Cuphead and Mugman
Going backwards, I would say you can kill the passengers just fine, being normal people walking around in their night clothes. The Traveler is a bit more difficult, as he has a sword and wind magic, but his ranged fighting is non-existant since the only ranged attack he has is a mini cyclone with a long cool down. Oliver has a much wider range of much more powerful magic, but is physically a kid (canon age is 12, but he can pass for 8 if I’m being honest here). He also needs a wand to do anything and only so much magical power that does not recharge easily. Then of course the Bean from Fall Guys is barely able to run without falling over, that is a pretty quick kill, while the Crewmates are quite squishy and easily killed themselves.
Maximillian and Monica are the first real fights here, as he has a gun as well and she has magic for long range fighting. That said, the choice of combat zone you selected gives you an advantage, as both of them have fighting styles that heavily favor wide open terrain, not a dense forest. I’m still giving you this win.
Sam is a… problem. You can kill him, no problem. The problem is he wouldn’t stay dead. I’m not going into the spoilers, but the metaphysics of Death Stranding has left Sam incapable of STAYING dead. You have no choice but to capture him alive, which us a tactic he specializes in himself. Again, his fighting style specializes in wide open areas, but his repatriation means you still need to get up close. You have a physical advantage in size to him, though, so you may still win if it came down to a fist fight.
Xehanort is also an issue. Like several earlier characters, he has magic for long range and is an expert fighter at short range. He is also well rounded in his abilities, so he wouldn’t be limited by the closed spaces. Unlike Sam, Xehanort also has a huge speed advantage over you and is very used to dealing with much larger opponents. While a gun of your firepower is stronger than most of his opponents at this stage in his life (by the time he is older, buildings being tossed around is more common) he should still be able to kick your butt. This is the first fight I’m pretty sure you would lose.
Frisk is the exact opposite. They are clever and good at making friends of enemies, but are otherwise a normal (albeit highly determined) kid. The twist is that they can have saving the game as an actual ability (4th wall break, ahoy!) If you are more determined than them, however, they wouldn’t be able to use that ability.
Finally, Cuphead and Mugman. About as fragile as you would expect sentient chinawear to be. You shatter them pretty quick, probably while tanking their rather weak bullets
So basically, my final verdict is that you can easily beat most of them, but a few give you trouble with one being a pretty safe bet to beat you.