This is literally a tactic employed by Ray Palmer, a.k.a. The Atom: he shrinks down to a tiny size, but his mass doesn't changenote Or, rather, he has just as much control over his mass as he does over his size, so it's basically whatever he wants it to be, which means he can pack a wallop... or tear through somebody like a freakin' bullet.
Al Pratt, the original Atom, was only 5'1". That's where his nickname originally came from - he was small. But he took up boxing and later actually gained super strength.
Similar to The Atom, anyone who uses Pym Particles (most notably, founding Avengers Ant-Man and The Wasp) can shrink down to the size of an insect while maintaining the strength of a normal-sized person.
One soldier holds off at least half a dozen Mundy rats and gets back to make his report on Bluebeard.
In "March of the Wooden Soldiers", at least half a dozen, mounts and riders, die as the soldiers pry out the pegs connecting the knee joints of the titular soldiers.
A defining trait of all of the Robins from Batman, especially Jason Todd and Damian Wayne.
Their adopted sister, the second Batgirl, is this even as a young adult, being 5'5" or shorter but physically stronger than almost any other member of the Bat-Family.
Wolverine. 5'3". One of the two or three most dangerous non-super-strong characters in the Marvel Universe in close combat. (He even beat the Hulk - check that, he almost killed the Hulk - once.) Wolverine's Healing Factor does give him limited super strength as well, particularly combined with his adamantium skeleton, allowing him to take fuller advantage of his muscles' capabilities.
His Opposite-Sex Clone/daughter X-23 is generally depicted as being even smaller, (both shorter and far more lightly built, being officially 5'1" and a rather slim, if athletic, teenage girl) and may be an even more dangerous fighter. Although Laura's skeleton isn't bonded with adamantium, as with Logan her Healing Factor pushes her strength somewhere beyond the human peak for a woman of her size. It's really saying something that in Marvel: Avengers Alliance she's considered a Bruiser. This puts her in the same class as Hercules, Hulk and Thor.
Alpha Flight's Puck. Shorter than Wolverine, hits just as hard. Even in a prequel story before he lost his height completely, fulfilled this trope.
Spider-Man, while average by real life standards (5'10"), is practically a midget compared to the vast majority of his allies and enemies, Wolverine being the notable and perhaps only exception. Spider-Man has the proportionate strength of a spider, and can lift hundred's of times his own body weight. He has been known to lift and use CARS as bludgeoning tools without effort.
In Ultimate Spider-Man Peter Parker stands at around a petite 5'5, making most people he comes into contact with tower over him. However, he is shown to lift cars and trucks with hardly any effort.
Rorschach in Watchmen is an unassuming man who stands 5'4, yet frequently kicks bar-fulls of ass. Interestingly, he wears thick-soled shoes to make himself look taller.
Lately, Jubilee. A petite teenaged girl who, on the New Warriors, used power gauntlets to become the most physically powerful member of the team. With her old powers, she was still quite the powerhouse. Basically, when she's really pissed she can take what started as a mostly harmless lights show Up to 11, resulting in massive kaboom. (Basically, she becomes her video game/animation self.) And these days, she's a vampire.
Here's an extreme example. In Peanuts, "World War II" (a.k.a. the cat that lives next door) is a vicious creature that Snoopy is afraid of (and yet someone that he always insults) who often rips his doghouse to pieces. The rare times they've fought have always ended badly for Snoopy... And yet, somehow, Woodstock won a fight with this cat! After it had beaten up both Snoopy and Linus, no less! How Woodstock did this is a mystery.
Molly 'Bruiser' Hayes from Runaways is a superstrong mutant and a preteen girl. Marvel's website actually named her the fourth toughest female on their roster, following She-Hulk, Ms. Marvel, and Rogue.
Astérix is drawn as smaller than most characters (and sometimes referred to as "the small one"), but turns into this when drinking the Magic Potion.
In a Garfield strip, Garfield climbs up a tree where a bird is singing, saying, "Ready or not, here I come!" Then there are sounds of a ferocious fight, and Garfield is thrown out of the tree, beaten to a pulp. "He was ready..." groans Garfield.
In the Marvel ComicsTransformers comic, there was Buzzsaw. From the show you know him as "the bird-thing we rarely see who looks like Laserbeak but in orange instead of red.'' But in the comics, he makes a habit of utterly handing full-sized Autobots (and more-than-full-size Autobots, such as OMEGA SUPREME) their skidplates. Worse, he's psychotic even by Decepticon standards: he considers himself an artist and the precise mauling of his enemies the ultimate in beauty. If you ran into him, you'd laugh at the Minicon-sized bird that's acting like he's going to fight you or something... for about two seconds. Then you'd find yourself being agonizingly turned into a gutted "masterpiece."
In The Transformers: More Than Meets the Eye, Tailgate is a tiny, good-natured Transformer, who - after gaining Outlier powers from a traumatic experience - becomes a powerhouse. At one point, most of the ship is in trouble because of Sunder, whose eyes can make a Cybertronian turn inside-out. After Rung blinds Sunder, Tailgate picks up the Rodpod - a Cybertronian shuttle that has enough room for twenty-odd full-grown Transformers - and crushes Sunder into scrap metal with it.
Cindy of Cindy and Biscuit is a pre-pubescent girl who regularly beats monsters several times her size to death with pieces of wood. Her Establishing Character Moment in the very first story has her hitting an alien over the head with a stick hard enough to smash its spacesuit helmet to pieces and utterly pulverise its head.
The Female in "The Boys". A teenage Japanese girl who is (maybe) five feet tall and a hundred pounds soaking wet, she is the biggest physical threat in a whole team of them (well, apart from Hughie). Frenchie even says that were it a straight-up fight between her and Butcher, it would be over very quickly, and in her favor.
One of the Guardians of the M'Kraan Crystal in Marvel is known as Jahf, who is a dwarf only 3 feet tall, yet capable of throwing down and beating the likes of Gladiator. Inverted with the next guardian, Modt, who is the size of a giant and 1000 times as strong as Jahf.