To elaborate, Medaka bypassed Takachiho's super reflexes by simply moving too fast for her opponent's body to react.
Zenkichi's fight with Munakata is this. Munakata is seriously badass with his Hyperspace Arsenal, but then Zenkichi one-ups him by countering every single weapon that Munakata threw at him! Which, mind you, involves sledgehammers, pistols, grenades, a bazooka, and THIS.
Zenkichi gaining an ability of his own (Parasite Seeing) and him using it to defeat all of Emukae's mandragoras.
And right after that he manages to convince her that her Minus wasn't such a bad ability after all.
HINOKAGE. He's so strong that people tend to forget him out of sheer fear, and yet he continues to protect and help everyone, knowing full well that his efforts will most likely be forgotten.
Kumagawa. Just... Kumagawa. Despite supposedly being the weakest, unluckiest being on the planet.
This guy took out a bunch of Abnormals like it was nothing. One of those Abnormals being a guy with superhuman reflexes.
His All-Fiction essentially allows him to warp reality. And oh god does he use it in the creepiest way possible. Like staying alive after impaling himself with a giant screw.
He's also unusually good at manipulating people, despite being a Self-Proclaimed Liar. Heck, he almost manages to recruit Kujira into his team!
His gambit in the Student Council Election Battle, wherein he volunteers to be the first to fight so that the rest of his teammates can take out Hinokage, Akune and Kikaijima who were, at the time, training in order to prepare for the next battles.
Kumagawa: "I want to beat those with friends when I can't have friends! I want to beat those who work hard when I can't work hard! I want to beat those who win when I can't win! I want to beat those who are happy when I'm this miserable! Even if I'm hated! Even if I'm despised! Even if I'm useless! I want to prove that I can be better than the main characters!
This guy forced Medaka to go all out. And this was after he gave up his reality-warping abilities. Wow.
In that same chapter, he explains that as the weakest being alive he knows everything about weaknesses, allowing him to instantly detect blind spots and vulnerabilities. It's also heavily implied that he succeeded in banishing an almost-certainly omnipotent person with just his aforementioned analytical skills and a simple Minus.
His mind games with Aka Aoki have to be seen to be believed. Just go read Chapter 105.
Though she gets back up and curbstomps him next chapter, and shows that she doesn't even need to see abilities anymore in order to copy them. Whoa.
Munakata's fight with Kumagawa.
Munakata actually managing to kill Kumagawa! Shame he's immediately one-upped when it's revealed that Kumagawa had managed to stay alive by retaining All Fiction. Somehow.
The Naked Apron Alliance's gambit in the Bloody Sevens game, a cunning ploy, that, for once, was not perpetrated by Kumagawa, but rather, Kikaijima! Rendered in her initial villainous version to boot.
Medaka winning a tug-of-war match against the entire school with enough force to send students hurtling into the air. Okay, maybe that's par for the course. What's better is that the last one holding on to the rope was Zenkichi, and he didn't let go for one second.
You know that the world of Medaka Box is bonkers when you learn that there's a voice actress who remodels her internal organs to be able to play any kind of role. Her first demonstration of her talent? Mimicking a piano. And actually sounding like one (or at least good enough to fool most people).
Zenkichi wowing the crowd with his harmonica skills. Even managing to make Medaka tear up!
Zenkichi's ultimate moment of awesome: winning against Medaka. Against. Medaka. Even Ajimu, our resident nigh-omnipotent being, thought it was impossible, and he did it. And he might have captured her heart in the process, too!
And the way he did it (according to Ajimu) was awesome and heartwarming: he appealed to the student body's compassion, and most of them listened.