Animation Bump: The animation for the Theme Tune (see below) was done by a different studionote Canvas Inc., who also did the title sequence for ProStars than the episodes proper, and it uses a clear, smooth, professional style. The animation for the rest of the show was anything but clear, smooth and professional, with errors that don't even need frame-by-frame analysis to spot.
Aside Comment: "This is easier than talking Kootie Pie into a shopping spree!"
Balloon Belly: Happens to Mario and Luigi when they activate P-Balloons once in separate episodes.
This also happens to Yoshi a few times when he overindulges himself.
Big Eater: Yoshi, obviously, to the point where he even puts Mario to shame. This is lampshaded at least a couple of times.
Broken Aesop: "A Little Learning": Bullying is okay, as long as it's to people who deserve it.
Calling the Old Man Out: Oogtar does this to King Koopa when he discovers he's giving Bob-ombs to the Koopa Kids as Christmas presents.
Cassandra Truth: In "The Yoshi Shuffle", Mario and Yoshi score the game-winning touchdown and Cheatsy the referee promptly calls them out for cheating. However, you can see Mario and Yoshi clearly go out of bounds to score, giving Cheatsy reasonable evidence to accuse them.
Casting Gag: Since Toad was left out of this series, production had John Stocker voice the replacement, Oogtar.
Cut Lex Luthor a Check: Koopa actually seemed to have a profitable, legit business going in "King Scoopa Koopa". Even the Mario Bros. were impressed. Of course, Koopa just had to go turn everyone into Chickadactyls For the Evulz.
Demoted to Extra: The Koopa Kids appeared less frequently in this series than in The Adventures of Super Mario Bros. 3, giving way to other evildoers such as Wizardheimer and The Dino Riders. Some episodes even had Koopa scheming on his own with little or no help from the Koopa Kids.
Koopa was subject to this as well. He was completely absent in four episodes and made brief cameos in three others.
Early-Installment Weirdness: In "Fire Sale", Yoshi doesn't talk like a baby. Also, assuming that the "Ice Land" featured in that episode is the same as Super Mario Bros. 3's Iced Land (or even our own Iceland), it's the only time in this show that the protagonists travel outside of Dinosaur World.
Funny Background Event: "A Little Learning": At the beginning of the "Rockin' the High School" sequence, a cave person jumps toward the ceiling, going airborne while the everybody else dashes for the exit.
Gasshole: Yoshi also burps several other times in the series, mostly after eating.
Leitmotif: Since the show re-arranges most of the music from the first two Mario games, the tunes are indicative of the character or type of environment that is currently on-screen. Examples: The Valley of Bowser theme playing when Koopa's castle is shown.
Limited Animation: Sometimes it gets to the point where you can't tell if what's happening is intentional or not.
Mutagenic Food: Eating enough Chickadactyl Eggs will turn the consumer into one themselves.
Nice Job Breaking It, Hero: In "Gopher Bash", The Mario Bros. succeed in rescuing the crops from Cheatsy but Yoshi eats the entire sack, meaning they have to plant everything all over again.
Off Model: The animation quality of the show was rock bottom to begin with, but was brought down ever further by outrageous animation errors that frequently pop up in the shorts, some of which are so blatant that you don't even need to freeze frame the cartoon to notice them. And Mario and Luigi still have the colors of their overalls and shirts swapped in this cartoon. King Koopa still remains off model in terms of coloring.
Happens in "Send In the Clowns", where Mario and the cavemen don't realize the clowns in King Koopa's circus are actually Rexes until one of their noses falls off.
Also happens in "Rock TV" when Koopa is in a paper thin disguise promoting the titular product. No one can tell it's him even though several of the shows he mentions even have the name Koopa in the title.
Pragmatic Adaptation: While not for the whole series, the episode "Send In the Clowns" explains why someone as mean and nasty as King Koopa would have a helicopter with a clown.