Basic Trope: A character who pulls far more than his own weight in combat.
Straight: Bob blasts through Mooks by the hundreds.
Bob depopulates entire worlds on a regular basis.
Bob is fighting against the whole world going against him, and doing a pretty good job at winning.
Bob is a skillful fighter, able to take on multiple opponents easily. But more than six and he's in trouble.
Bob wasted hundreds of enemies, though he was mostly using ambushes and traps to get kills while using stealth and superior mobility to avoid retaliation. Once the enemy successfully ambushes him and forces him into a straight fight, he's toast.
Bob has a vast array of powers that make him ridiculously powerful compared to a normal human.
He's just that good.
He specializes in attacks that affect a huge area, maybe to the point of being a Person of Mass Destruction, and most of his battles are in wide-open areas where the enemy can Zerg Rush.
Bob is a trained warrior, while mooks are an unprepared bunch of peasants wielding blades on sticks.
Bob and his allies are the ones getting blasted apart by a small number of Elite Mooks.
Bob manages to beat up 50 mooks, but the 51st took him down easily.
The mooks had been ordered not to put up a fight, but they did anyway.
...Until his superpowered side kicks in.
Alternately, they were ordered not to put up a fight, but Bob still has no trouble fighting off the wave of ones that weren't.
Parodied: Everybody, including the bad guys, treats Bob as a One-Man Army, even though he really isn't and makes no secret of this.
Bob racks up massive amounts of kills, and then it was discovered he had help...but only on the last of the 1,000 battalions...which were ordered not to put up a fight...but did anyway...even though they had no weapons or training....
Bob has Me's a Crowd as a superpower, and uses Doppelganger Attacks to take down a great number of the enemy. Technically, he fought them off by himself, but at the same time, he was not alone.
Averted: Bob's combat abilities are on par with the rest of the cast.
"We need to show the audience how awesome our hero is, so let's have a scene of him taking on a few hundred mooks by himself".
Discussed: "Legends say the Mountain Warrior slew ten thousand foes in a single day".
Conversed: "Exactly how many kills have you racked up over the course of this game?"
Everybody Bob knows lives in fear of him, and the government has prepared deadly countermeasures in case he ever switches sides.
Alternatively, killing hundreds of people has devastating effects on Bob's psyche.
When Bob gets somehow killed or dies, perhaps of old age, the government realizes how screwed it is because its Redshirt Army has nowhere near similar fighting ability. Easily Conquered World ensues.
Bob may kill hordes of mooks with ease, but he's ultimately Just One Man and can't be everywhere at once. The Enemy adopts a strategy of attacking on multiple fronts simultaneously, which Bob can't defend against.
The Enemy decides to Nuke 'em since it can't beat him conventionally.
The government, due to incompetency, never uses said countermeasures, allowing Bob to wipe out armies anyway.
All of his friends have been killed while trying to be this trope, so Awesome Bob goes into Tranquil Fury on all of his enemies and murders the lot of them.
Bob breaks down for a while, but recovers and comes back even deadlier.