Live-Action Plot: The Mario Bros. are helping their new neighbour unpack and acclimate to the neighbourhood. It turns out this guy is one “Dr. Frank N. Stein,” and he’s brought a dangerous monster with a bad brain along with him. Eventually, Luigi heads out with the doctor to do some grocery shopping and find a new brain while Mario takes a nap alongside the wretch. Of course, his brain is accidentally switched with that of the monster’s during this nap. No worries though, a round of head bonking rights the problem.

Very Special Guest: To my very great relief, this episode correctly identifies Frankenstein as the creator, and his monster as a separate entity. Sadly, the abomination is represented as a mindless, zombie-like creature, rather than the intelligent but bitter man of the novel. One quirk I did notice as to the naming, or perhaps a slip-up, was a moment in which the doctor calls his monster “Frank.” Maybe that was some inaccurate ad-libbing from the actor.

Animated Plot: The Bros. are once again in pursuit of Koopa, who has kidnapped Princess Toadstool and is making off with her in a river boat. The Marios team up with Mark Twain, who is also chasing Koopa. Mark’s not trying retrieve something from the terrible lizard, but aims to beat him in a seemingly ongoing race down the river for the title of King of the River. Along the way, Koopa tosses a Black Hole Bob-omb down river, creating a massive pit that stands in the way of Mark Twain’s boat. Luckily, the brothers are plumbers first, and quickly redirect the river by building a massive pipe system around the hole. In the end, the brothers catch Koopa, save the princess, and Mark Twain is made king. Oh, and Toad makes a Pee-Wee Herman reference at some point.

Horrible Stereotype Alert: Once again, the Italian jokes have really been paired down, this time to almost nothing. Mario is still desperately hungry all the time, and fat jokes are made at his expense. A new line of insult is opened up in this episode against Mario, and it’s about his brain. Dr. Frankenstein and Luigi repeatedly make remarks about the undesirability of Mario’s brain for the monster, implying the plumber’s stupidity. That’s just mean.