I want to know what you expect from a story that suggests the mc will be fighting hordes of monsters alone. You can skip suggestions like a good system, not op mc, doom. What I want is a good or great antagonist, even more so than the mc, and a plot that includes more than actions, a bit of drama, some slice of life, and adventure.
Mc getting his butt kicked and almost couldn’t escape with his life at the beginning and having to be saved by someone or MC hiding somewhere waiting for the monsters to pass, but improve later on (will still get injuries cause like come on, fighting a whole group of monsters. Be glad that you didn’t die under their dirty claws) due to the help of a team or someone who are planning to use MC in exchange for something valuable from a monster. Kinda something like that, idk.
This is gold. We can even kill him directly to kick his pampered ass. Of course, he'll be revived with penalties. I'm going to write this one down: Kill him more often. Thanks.
A man of culture, that is. As for your antagonist, I suggest you write about a character with beliefs and goals that he'd do anything for, and not about someone that is bloodthirsty and edgy, but rather one that treats killing as only a sort of means to exact his goals. In addition to being a character that is unscrupulous in doing things. In other words, whichever method would let him reach his goals the fastest, he would use it.
So someone like Thanos. Basically, the demons will need a good reason besides anger to kill all humanity. Something like the demons need to kill humans to prevent some other thing. Gotcha
SO Giganteous boss monsters with some depth Depth (something basic): Five demons clans, one for each element. Their world is dead (Cliche), broken by something else (no idea). They were normal once, another civilization before they had to fuse with the elements to survive. The fusion changed them. LIfe can turn them back. They are in contention. One planet, five groups. The mc is an outsider. Kinda meh. I don't know. needs refinement.
It would depend on my expectations of the MC in question. If you have written chapter after chapter of the MC beating young masters and their father's best men it would be disappointing if he didn't wreck shop. By the same token if he is one of those wishy-washy overly humble virgins that avoids fights it would be equally disappointing for him to suddenly grow a pair and clean up the monsters.
Additions: Each element represents a mental state. Fire: Anger, best for being soldiers. Water: Patience; suited for stratigens. What if he's... alone? Think 'I am legend' kind of alone
If I was to suggest a method for a MC to fight "hordes" when their absolutely alone, I would go the "stealthy, trapped, hit & run" route. While I haven't written anything yet, I have designed various worlds and power systems for those worlds, and every time I try to include something that'll allow MC to become OP, I end up wincing and backing off because somebody else would have already exploited that, so I can't bring myself to suggest that. However, stealth, traps, and skill at running away is perfectly reasonable. Stealth to allow you to set things up before hand, traps to kill enemies, skill at running away to both lure enemies into traps and to disengage from fights when your stealth or hiding spot fails. Only fight when it's one-on-one, and preferably only if the enemy is already too crippled to fight back. If something feels strange or wrong, bugger off and pick a different fight another day. Even if you only succeed in killing a single enemy at a time, that's a success at harming the enemy. The challenging thing is that, in addition to them fighting hoards, you've also added into this thread the possibility of them fighting giants, or even giants of giants and beyond (for what I'm discussing here, Giants would have about the same mass as an Elephant, while a Giant of a Giant would have the mass of a Whale, with beyond being beyond the mass of the largest whales). That requires completely different thinking, and I'll say that should be something the MC builds their way up to over in-story years, and only succeeds in killing one of elephant-mass sized giants, before getting it stolen by one of the whale-mass sized giants that MC had never noticed before, just before the story ends with the MC realising that they were even smaller than they thought they were.
Unfortunately, I can't do that because.. demand. It's something I've come to notice after a handful of failed projects. You have to supply what is demanded. Making the mc an assassin/thief/builder of sorts would make for a rather slow story. I have written too many of them, good plot, good character, slow stories that people don't want to read. And I've already created the system. It's the first thing I did. I made it compact and precise. No bloated skills like cuckold resistance and Erectile correction made their way into... jk. The system is great, perfect to fight off monster hordes. That being said, your suggestion made me realize another important thing besides the characters, which is the terrain and its importance. Mc might not go around silently killing monsters, but he will use the terrain to his advantage. I would not have realized this until it was too late. How one uses their power represents their strength, not how much mana they have. (I'm going to refine this line and use it in my synopsis.) Thanks for the help.
Angry Aggro Afro Assassin. Kind of like the "I'm a medic, but..." meme, just put your MC in berserk/confusion/cursed state or something and let him or his sanity profit from kicking butt and chewing monster gums