About halfway through "Air Batter", the camera starts zooming in and out, and the batter will end up wearing various silly masks on his head.
There's something hilarious about the goofy noises the ghosts in "Shiro Obake"/"Sneaky Spirits" make, both the "oink-oink" sounds they make when sneaking and the needlessly dramatic moans they make when successfully shot.
Falling into a pit in "Night Walk" results in instant stage failure. It also results in the game flatly stating the obvious to you on the result screen:
You fell in a hole.
The same feat can be repeated in the "Night Walk" Mini-Game Credits in Fever. When it happens, Miss Ribbon and Cam look down at where you fell in surprise.
Rhythm Heaven/Rhythm Tengoku Gold
The bonus material for "Freeze Frame" reveals that the woman who passes by at one point is the photographer's girlfriend, who was feeling ignored and deliberately photo-bombed him in order to get his attention.
Rhythm Heaven Fever/Minna de Rhythm Tengoku
"Donk-Donk". It's so completely bizarre that the American version of the game doesn't even try to describe what's going on.
Watching barnyard animals catching the kicked footballs in "Double Date 2".
During Remix 7, the action briefly switches back to Karate Man... who doesn't actually do anything, he just lays there watching TV for a bit before the remix switches to another game. Even funnier is that he's apparently watching the Karate Man game fromTengoku.
"See-Saw". See and Saw's job is to test see-saws to make sure they work properly. Apparently, testing them consists of repeatedly jumping up into the sky and back down at explosive speeds to hard rock music. Then they explode at the end, presumably due to awesomeness overload.
The Police Call code SEESAW, consisting of See and Saw jumping up and down on a seesaw at an accelerating tempo until they explode.
Blink and you'll miss it: Remix 4 recasts the Wrestler from Ringside as a samurai, complete with a sword in its sheath at his back. One of his poses reveals that the sheath is taped to his back.