The NES version's slightly chibi-fied characters have a cartoonish Volumetric Mouth that takes up most of their face whenever they get attacked or walk off a ledge (and sloooowly fall to the bottom).
The fourth wall-breaking ending credits song ("Dared to Dream") to Double Dragon Neon, wherein Skullmageddon sings about being defeated by the Lee brothers. The funniest part comes at the 1-minute mark, when he sings "Here's a medal for your victory" and the Achievement Unlocked/Trophy Unlocked dialogue pops up.
Skullmageddon: I'm your worst nightmare, Skullmageddon! Have at you!
Right after you press start for the first time in the 360 version, you get an achievement called Skullmageddon's Curse that's worth 1 GS, with the description "Nyah ha ha! Now finish what you have started!": a lot of people like to keep their GS divisible by 5 and the score can only be evened out by getting the achievement described above, which involves defeating him.
Right before you encounter him for the first time, you can find a hair pick from a barrel: if you throw it at him, it'll pin down his hat on his head, making it so that he can't use any attacks that involve removing it until he takes it off while complaining how he could be done in by such a mundane item.
When trying to kill the Lee brothers with a helicopter, he's heard saying "what do you mean helicopters can't fly upside down? Of course they can!" and then proceeds to do just that.
If you pause the game while fighting him, he comments on it in a variety of ways:
"Oh fine, just pause the game!"
"I was just about to swing my sword!"
"I'm flashing orange so quickly! Quick, just hit me a few more times!"
"When I'm about to swing my sword, just punch me and I'll stop! I'll save you a trip to the Internet!"
When the pagoda launches into space and you have to walk outside.
"Better hold your breath dude! This is a hard vacuum!"
Made even funnier by the fact that while outside, you can viably see the Lee brothers have their cheeks puffed out.
The fact that you revive your brother by using a pencil to fix their mix tape. This was even referenced by the Limited Run Games release for the Switch version, as two of its items are a pencil and a mix tape for the game's soundtrack.
The Killers in Rise of the Dragons are based in an abandoned skyscraper with the elevators back in working order (a good thing, considering how the floors themselves have their share of gaping holes). The humorous part is that the elevator you take to the first boss battle there still has its Elevator Music running, at odds with the Killers' military roots.
