Much of the lore and visual design out of Super Mario Bros. seems like it was developed during a fever dream or drug trip: a turtle king kidnaps a mushroom princess, leading to a heroic plumber to save the day by jumping on and throwing throwing fireballs at turtles, mushrooms, squid, and beetles.  It's easy to mark this all down as "Games: weird, am I right?", but over at Reddit in the Ask Historians section, the question about whether or not any of the elements from Super Mario Bros. and Super Mario Bros. 2 have any Japanese cultural significance.  The answers provide some interesting information that while seemingly common knowledge to the long-time gaming community is written from a more academic stance than your average list of "didja know?" gaming factoids.  Best of all, it cites sources.

Super Mario Bros. features surly traitor-mushrooms, green and blue turtles, black turtles that can't be hurt by fire, hammer-throwing turtles and giant, spiky dinosaur turtles, along with red-and-orange mushrooms that make you grow, green-and-yellow mushrooms that give you a chance to recover from failure and bouncing stars that make you impervious to damage.

SMB2 has a pink, cross-dressing lizard that spits eggs, and is arguably even weirder than SMB1.

How much of these were riffs on Japanese legends (or perhaps something more contemporary?) and how much was just weird videogame stuff?

The answers touch on Mario's Jumpman origins, Bowser's original ox-like design, the ever-assumed link between Super Mushrooms and psychedelic drugs, how level design trains players, the ever-present tale behind the Lost Levels, and other interesting background elements.  It's definitely worth a read even if you know all of this stuff already.