So, I have a scene where one of my characters shows up to fight a pretty strong enemy. The length of time from when he enters, and the enemy is killed is fairly short for how strong I want the enemy to be, but said enemy had just spent some time beating up on several other characters. The character who beats him does get some wounds, and had already lost to the enemy, but I feel that it'll make this character look a bit too OP. Thoughts? Can an enemy be beaten too quickly? Note: This enemy is a mini boss if the main enemy is the dungeon boss.
In real life most fights are over in less than a minute. Pretty much the only exceptions to this are sport fighting where opponents are evenly matched and have to abide by a set of rules, and really bad fights where no one knows what they're doing and spend more time mouthing off and awkwardly grappling than fighting.
It's a real kind of "Oh my gosh this guy is way too strong what am I gonna do?" Then the way too strong guy starts goading his enemy and so he something happens and power boost, etc, etc, way too strong guy killed in a rage. But I should have mentioned that the power boost I'm referring to has happened before, and only works because of the nature of it's power (i.e. it's electricity and the way too strong guy dies from a shock straight to the heart).
That - generally a lot less than a minute if one opponent knows what they are doing. The only other exception are squad or platoon level firefights where you are shooting it out with an unknown number of enemy and you have multiple points of fire ... that can go on a fair while if both sides have grabbed some cover.
Of course he didn't go super saiyan, that would be foolish. Besides, he doesn't even talk in this fight, much less scream his head off for 5 episodes.
I think a lot of factors come into determining if your enemy was defeated too soon. How long has your Main Character known about this enemy? What part of your story (beginning, middle, end) does your character defeat the enemy in? And is this enemy a sort of stepping-stone that leads up to the real major conflict? If this is your final conflict -the climax of your story- then you might want to invest some time in drawing that scene out. I, personally, find it rather irritating when the MC can defeat a big powerful enemy in a short amount of time with little-to-no injuries, it lacks any feeling of being real. If it's just a smaller enemy leading up to the bigger one, then you could probably get by with defeating the enemy fairly quickly, as long as it's done in a plausible way.
Well, they've fought before. In fact, in the first encounter, this character lost. This particular enemy is fairly strong, able to take on the entire main cast easily (this is mostly due to the fact that none of them are very strong yet). The main reason that this character can beat him is that he gets pretty strong when he's backed into a corner. From what I just said, you can probably extrapolate that he is not the main enemy.
He heard some rumor about a really strong fighter (which is supposed to be one of the main characters) and doesn't he doesn't have any empathy. So when he realizes that he isn't as strong as the rumors say he is, the enemy just decides to kill them for being weak because "Weaklings shouldn't pretend to be strong. Whelps like that belong in the dirt!". (Yes that line is supposed to sound pretentious)
I think martial arts are mostly about defense. Most trained fighters can't hit harder than a football player swinging wild hook punches or trying to tackle them through a wall. Martial artists get so good at defense that it is difficult to put one another down, and they know that if they over commit to a hit and miss, they put themselves in danger. The other reason why sports fights take so long is because the combatants can't back down. In a real fight, if you hit someone once or twice, unless they hate you, they will try to find a way out of it. Most people quit as soon as victory isn't assured or they are getting hurt. Truthfully, they could go a lot longer provided they don't get a concussion or the wind knocked out of them. The rules don't have much to do with it. Two pro MMA fighters having it out in a NHB match could still take twenty minutes.
I mean generally speaking if it's a mook then generally speaking your talking about a short fight. Maybe about a page or two tops, depending on how much detail your putting into this fight. Since your saying miniboss, make sure there is some white knuckled tension before defeating him. You don't want this person to say "Oh no what I'm going to do" then a few punches dead. If your team is struggling, this person is going to struggle as well, and then pick himself back up. For reference watch any Indiana Jones fight scene with essentially a miniboss. He gets his ass kicked, and then comes back on top.