Be Cool, Scooby-Doo!: Unlike Mystery Incorporated, Rose wants to profit off of mystery-solving rather than doing it for fun or for the greater good.
To Daphne. The both of them are/were friends of Fred, are girls, and share the same voice actor, but Daphne is into having fun with her friends, which is why she's into mystery-solving, while Rose is a selfish gloryhound who does mystery-solving to satisfy her ambitions.
To Professor Huh?. He was an evil villain years ago, but he eventually learned to regret his crimes while in prison. Meanwhile, Rose's ambition to become a celebrity eventually destroyed the few morals she had as a child, resulting in her becoming an unrepentant villain who won't hesitate to ruin the lives of others for the sake of ambition.
'Scooby-Doo on Zombie Island'': Lena and Simone contrast each other somewhat in personality. While Lena is friendly and is happy to invite Mystery Inc to the island, Simone is strict and is not as enthusiastic about them being in her house. They also somewhat differ in appearance, with Lena appearing younger, dressing in red, and being a brunette while Simone appears older, dresses in blue, and is a blonde. In addition, while Lena typically hunts down victims when visitors become scarce, Simone Lenoir remains at Moonscar Island while she is doing so. Finally, while Lena is concerned when Jacques is being attacked by zombies, Simone decides that draining Mystery Inc is more important so that they don't miss their deadline.
Bill Nye for Jonathan Crane. Both are scientists, and both talk about logic and reason. But Nye is helpful and supportive of Mystery Inc., while Crane is antagonistic and villainous. At least until he distracts the Alpha Pumpkin to defeat a common enemy.
Velma and Crane also foils to each other, with Jonathan Crane embracing fear (to the point of trying to make it his gimmick) while Velma denies her fear in the name of "rationality".
Mayor Fred Jones Sr. to Marcie Fleach/Hot Dog Water.
Both were the Sixth Ranger of the Mystery Inc. of their times, although this was a brief venture. At some point, they became the Sixth Ranger Traitor, though later redeemed themselves by helping the new Mystery Inc.
Both became enemies to their respective Mystery Inc. after doing a "Scooby-Doo" Hoax and ended up donning the costume for two major events. Mayor Jones only got caught after the second time, and Hot Dog Water got caught the first time.
Both initially did their "Scooby-Doo" Hoax out of greed (though Hot Dog Water was more justifiable) and used scamming the first time, though this later evolved into them getting involved in a grander scheme.
Mayor Jones tore apart the original Mystery Inc., while Hot Dog Water commits a Heroic Sacrifice to let the new Mystery Inc. survive.
Both are book-smart, if inept with social skills. Their knowledge has played a part in the plot when they worked with their respective Mystery Inc.'s, as it allowed Mayor Jones to take advantage of the original Mystery Inc. while Hot Dog Water becomes a genuine help to Mr. E & the new Mystery Inc.
Mayor Jones is charismatic, though the people that have interacted with him the most know that he's actually a self-serving Jerkass. Meanwhile, Hot Dog Water is an outcast, but her friendship and partnership ends up becoming invaluable.
Mayor Jones is from an upper-class and is rich, while Hot Dog Water is poor. Mayor Jones attended Darrow University for college, while Hot Dog Water's poverty situation is bad enough that her parents are worried that they won't have enough money to send her to one.
In addition, Mayor Jones dresses in a suit (or that one time, a nightgown), while Hot Dog Water dresses in worn-out clothes.
Mayor Jones wears Jade-Colored Glasses while Hot Dog Water wears red-framed glasses.
They are both close to the Gang in some way, except Cassidy is supportive of them while Mayor Jones usually is not. The fact that they of all people hold dark secrets is what leads the Gang into Heroic BSoDs.
Mayor Jones was the Older Sidekick to the original Mystery Incorporated, and Cassidy is the Older Sidekick to the new Mystery Incorporated.
Both revealed the truth about their true identity and actions at night at the Spanish church in the endings of the final two Season 1 episodes. The reveal of their lies pushes their successors away and they beg them not to leave them. In Cassidy's case, it's because she fears for their safety. In Mayor Jones's case, it's because he doesn't want Fred to abandon him. They were also present at each other's confessions without the other knowing — the Freak was watching Cassidy confess from a distance and Mayor Jones confessed while Angel, whose true identity was unknown to him, was present.
They may be Ambiguously Gay. Angel is on the receiving end of some interesting admiration by Principal Quinlan in "Mystery Solvers State Club Finals" (although this ended up being All Just a Dream), and Mayor Jones has some interesting moments with Sheriff Stone, such as dancing with him under Aphrodite's love pheromones in "Where Walks Aphrodite".
Marcie design is meant as a contrast to Velma's Mystery Inc. design. She is slender, her glasses are armless with yellow lenses, wears a sweater that fits poorly and her hair are oily, wavy, long and held in place with plastic barrettes instead of bows.
