These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Gash has horns on his head when Kiyomaro is forced to wash him after a battle. Other Mamonos have horns, yet it is never brought up ever again.
The demon Momon was known to let out "kikiki" like sounds, akin to a monkey, but suddenly begins talking multiple volumes later. No one questions it.
One of the manga chapters is completely dedicated to a weird dream Kiyomaro had. It involved the reappearance of many characters (like Kiddo, D'artagnan and Leila), Sunbeam dressed as a fairy, "Manly Brago" teaching how do do "Silly Juggling" and many characters slapping Kiyo silly with various items. Apparently Kiyo loses his answer-talking ability for a while after having it, but the dream itself is never mentioned again.
Complete Monster: Zofis. A FreezaExpy who horribly Mind Raped both humans and fellow mamodo, both for practical reasons and For the Evulz. He expresses enjoyment in being able to control the hearts of others, and uses the fears of his followers to keep them in line. Completely selfish, petty, and sadistic, he's even referred to as being the worst of the worst by many characters. And he never shows any remorse for his misdeeds, only giving up in the end due to cowardice, which is also the only way he gets to keep his life once back in the mamodo world.
Clear Note was so thoroughly malevolent that Gash's ultimate spell, which destroyed only what was evil, erased everything that defined his person, leaving only his... soul, or whatever, to reincarnate as a different being.
The final chapter casts doubt on how completely monstrous any of the enemy characters (except the abovementioned two) really are, as the main characters are shown to have made friends with, or at least tolerated being in the same room long enough to have a photo taken with, all of them. Even Demolt showed up, making a peace sign and grinning like an idiot.
Crazy Awesome: The entire series and almost every attack in it, particularly Kanchome's. Almost every single minor character has some kind of crazy attack, too.
And a good example of this? Sunbeam spent ten months in Africa. Immediately after he comes back...well...rock and roll!
"With the dashing beauty of the Johnson located in my crotch!"
What about Zatch and Kiyo's battle against Kanchomé and Folgore in KIYO'S BEDROOM? With Suzy sleeping though the entire thing?
Ensemble Darkhorse: Victoreem, for... well everything. On top of his generally memetic theme, that utterly batshit song, and general ham, he's voiced by none other then Norio Wakamoto. His popularity is lampshaded repeatedly in omakes and the ending of the manga.
Growing the Beard: In the case of the anime, it takes a long while for the series to really take off and become something epic...until episodes 44 and 45, which features a brutal battle that Kiyo and Zatch flat-out lose. Shortly afterwards we're introduced to the stone tablets of 1000 year old mamodo in episode 48, and it just keeps going from there!
Villain Sue: Depending on who you ask, Clear Note is either a Villain Sue or an intentionally over-the-top parody of Villain Sues. He's a BishōnenGeneric Doomsday VillainDiabolus Ex Nihilo who makes his completely unforeshadowed entrance by beating Brago (until then the strongest character) half to death, defeats the Supporting Leader despite the fact that said leader's skin is explicitly resistant to his powers, comes back stronger every time you beat him up, is a Hero Killer (including one kill from thousands of miles away while critically wounded), and ultimately required what seemed suspiciously like an Ass Pull (it was foreshadowed... over three hundred chapters prior) to finally defeat. Whether all of this is annoying or darkly hilarious, again, depends on who you ask.
Wangst - Gash/Zatch can go a little overboard with his crying sometimes....