You'd Expect: That they'd follow him down the pipe back to his castle and teach him a lesson.
Instead: They let him get away. In one episode, they are even shown standing on one (granted, that was an animation goof but still).
However: Koopa probably has guards on the other side of the warp to deal with anyone who follows him.
"The Great Gladiator Gig": During the battle against Tryclydius, Mario cuts Luigi from a net by using a sword.
You'd Expect: That Mario would continue to fight Tryclydius by using his sword.
Instead: He tosses the sword to the side.
"Love 'Em and Leave 'Em": Queen Rotunda plans to give Prince Pompadour a Passion Potion, which she hopes will make him confess his love to her. She demands the Marios to make her a dessert for the wedding, pistachio ice cream laced with hot peppers. After trying some, she shouts for water.
You'd Expect: Mario or one of his friends to rush off and get the queen some water.
Instead: Mario snatches the Passion Potion off her throne for her to drink. She then falls madly in love with the first person she sees...Mario. Oops.
"Quest for Pizza": In Caveman Land, Mario has been knocked out cold by a snakebite and the only thing that can revive him is the smell of pizza. His friends start making one in the shelter of a city concealed by a waterfall. While picking tomatoes out in the open, they are ambushed by Alley Koop but leave him distracted long enough to get away safely.
You'd Expect: For the gang carefully consider how much tomatoes they can carry while keeping their hideout a secret.
Instead: They leave a trail of tomatoes into the waterfall. Alley Koop discovers this and has Mousersaurus reroute the waterfall to flood the city, ruining their pizza.
Adventures of Super Mario Bros. 3
"Sneaky Lying Cheating Giant Ninja Koopas": King Koopa has Luigi, Toad and Princess Toadstool trapped in a cage in his throne room, and his sons-turned-giants are present. Mario arrives and sneaks up, getting to the wands that King Koopa used to turn the Koopa Kids into giants and Prince Hugo into a poodle.
You'd Expect: Mario to snag the wands and use them to turn himself into a giant (or anything that could beat the Koopas) and/or revert the Koopa Kids back to normal.
Instead: He switches the wands' jewels and tries to trick King Koopa into using them on him, so that he would use the wrong wand and transform him into a giant that could then fight his sons. Granted, his plan worked, but it was unnecessary, and he got lucky that King Koopa didn't notice that the jewels were swapped (especially since they had different colors). Also, he wouldn't have needed to fight the giant Koopa Kids if he had used the wands on them.
Instead: It doesn't pass through his mind and his sons are forced to fight Mario. In the midst of this, Princess grabs a wand, using it to revert his sons to normal size and the Koopas get the heck out of there.
"Reptiles in the Rose Garden": Mario and friends see Koopa's Doomship hovering overhead.
You'd Expect: That they'd just make a run for it.
Instead: They stand motionless, somehow avoiding getting shot by the ship's gunshots, and as a result, get captured by the Chain Chomps that King Koopa sends down after them. They can't even warn the USA that the Koopas are coming.
"The Beauty of Kootie" is full of these. It starts when Mario and Luigi find Lady Fettuccini Alfredo (Kootie Pie in a human disguise) in the basement of the Sultan's castle. Mario falls for her but Luigi notices she has a tail and wastes no time revealing this.
You'd Expect: Mario to catch on, too, and realize something is fishy with this dream girl.
Instead: He ignores her tail the whole time and doesn't discover she's really Kootie Pie until Cheatsy changes her back.
Compounding It: Being Card Carrying Villains, the Koopas are subject to these moments. This is evidenced when Mario turns Luigi into Casanova Koopa with one of the Koopa Kids' lost wands.
You'd Then Expect: Kootie Pie to act suspicious, knowing she had easily tricked Mario with the same exact scheme.
Instead: She instantly falls for Casanova hook, line and sinker.
It Gets Worse: With Princess, Toad, the Sultan and a guard locked up, Luigi requests some privacy when Cheatsy asks who this mysterious Koopa is.
You'd Then Expect: Kootie Pie to have Cheatsy guard the prisoners while she and "Casanova" have their alone time.
Instead: She releases the prisoners in a fit of rage. While she and Cheatsy are distracted with Luigi, Mario and the others set up their trap.
"Never Koop a Koopa": Koopa announces that he and the Koopa Kids are admitting defeat and moving out of the Mushroom Kingdom. He hands Princess Toadstool the key to his castle as a token of forgiveness. After he disappears, Luigi tells her that she's being set up and to dispose of the key.
You'd Expect: Princess to trust Luigi and determine that all this is indeed too good to be true.
Instead: She talks the Mario Bros. and Toad into visiting the castle with the key in her possession, thinking she can turn Castle Koopa into a retirement home.
"Toddler Terrors of Time Travel": King Koopa and Kooky plan to trap the Mario Bros. in Brooklyn by blocking the only way they can escape, a woman's drainpipe that leads to the Mushroom Kingdom. They don plumber outfits and introduce themselves to the lady.
You'd Expect: That she'd catch onto them being costumed plumbers and call someone else to fix her plumbing or, better yet, alert the police.
Instead: She invites Koopa and Kooky into her home where she reveals a problem with the same bathtub drain that brought them there. The two Koopas proceed to clog it with anything they can find.
"Oh, Brother!": Mario and Luigi have a heated argument, with the latter threatening to walk out of Toad's House where a thunderstorm (created by Kooky) is brewing.
You'd Expect: Luigi to realize that going outside in the middle of a thunderstorm isn't a safe thing to do and maybe try to patch things up with Mario.
Or: For Luigi take a Frog Suit at Princess Toadstool's request since it had been raining nonstop for two weeks by this time.
Instead: Luigi storms out of the house without a Frog Suit, claiming he doesn't need one. Mario then goes after him without a Frog Suit as well and winds up getting captured by the Koopas.
"Mush-Rumors": The beginning where Norman inadvertently drives his family from Kansas through a Warp Zone en route to the theme park they're visiting.
You'd Expect: After taking a quick peek at the unfamiliar scenery, to turn the car around (or at the very least, have his wife and kids tell him to do so) and find a different way to the park.
Instead: He keeps driving and, with the wife suggesting they pull over and ask for directions, assumes the family is in Iowa (a state that does not border Kansas).
You'd Also Expect: Norman to pay attention to the road.
Instead: He gets distracted by the scenery and hits some blocks, crashing the car.
"Crimes R Us": All the Koopa Kids get one when Crimewave Clyde shows Kooky how to bust open the Mushroom Kingdom Treasury doors with a Bob-omb.
You'd Expect: For Kooky to go on with Clyde's instructions and the rest of them to carry out the heist as normal. Once they've finished, they can reveal Koopa's double cross to Clyde when he least expects it.
"Fire Sale": Mario, Luigi, Princess Toadstool and Yoshi have cornered Kootie Pie inside Ice Palace which is beginning to melt due to Mama Fireplant's tirades. Mario, Luigi and Princess have all been frozen by Porcupine Fish, leaving Kootie Pie to deal with Yoshi.
You'd Expect: That Kootie Pie would simply stay put and perhaps taunt Yoshi in hopes that he will also step on a Porcupine Fish if he chooses to run toward her. In addition, Yoshi is afraid of water so he may panic and accidentally touch one.
Instead: She goes after Yoshi and steps on a Porcupine Fish, enabling him to rescue Mama Fireplant and his friends before the Ice Palace collapses.
The Result: Kootie Pie becomes frozen from the shoulders down in a block of ice. Her screams are unanswered because her Koopa Troopa minion refuses to help her.
"Send in the Clown": Luigi, after seeing a poster for Koopaling Bros. Circus, tells Mario, Yoshi and Princess that King Koopa may be luring the cave people into a trap. They take a Star Path to Neon Castle and find the circus tent.
You'd Expect: For them to round up the cave people and leave immediately.
Instead: Mario persuades the gang to watch the show together with the cave people. Despite Luigi's suspicions, the heroes don't discover they're in trouble until a nose falls off one of the Rex's clown disguises.
"Ghosts 'R' Us": The Mario Bros. and Princess have been caught by Wizardheimer in the Enchanted Forest. He threatens to blow them up with a Bob-omb if they don't go in a warp pipe leading to his haunted house.
You'd Expect: For them to just run like the dickens since they're in a huge forest.
Instead: They enter the pipe.
"The Night Before Cave Christmas": Koopa is holding a present that Oogtar has spoiled, a Bob-omb that has lit its fuse.
Then: For their science fair project, Hip and Hop build a volcano.
You'd Expect: Well, anything other than how they demonstrate it below.
Which Is: Rigging the volcano to have real lava squirt out of it.
Even Worse: King Koopa intervenes and accidentally causes Hop to release huge amounts of lava which destroys the school and causes Princess to expel Hip and Hop.
While All This Has Been Going On: The Piranha Plant that Hip and Hop planted to sabotage Oogtar's "eggabaga" project grows large when Oogtar adds fertilizer to get an edge over Hip and Hop's volcano. During the chaos that ensued when the volcano errupted, the Piranha Plant runs out of the school and eats Koopa, Hip, and Hop. Yoshi then walks up and eats the Piranha Plant. He sits there with a bloated stomach, complaining that he doesn't feel good.
You'd Expect: Mario et al to encourage Yoshi to deal with it and let him digest, thus effectively killing off their archenemy and 2/7ths of his children.
Instead: The Princess directs Yoshi to inexplicably spit Koopa, Hip and Hop (who logically should still be inside the Piranha Plant) into a pipe.
Well, it's pretty doubtful Mario and Toadstool would want to resort to killing the Koopas (particularly the children) in order to be rid of their aggression. Aside from this being a kid's cartoon, Mario and group are simply too kindhearted and not cold enough to do that sort of thing.