These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Hilarious in Hindsight: Mama was simply an Action Mom before DDP got ported to the U.S. and her sprite was replaced with Luigi's. Surprisingly, a few years later, the animated version of Super Mario World launched an episode called "Mama Luigi", which would later become an internet meme thanks to various YouTube Poop videos.
Imajin was originally The Mario of this game. Guess who replaced him.
Nightmare Fuel: The 1-Ups in this game were the head of your chosen character. SMB2 changed this to the iconic 1-Up Mushroomnote Although, in this game they were simply orange-brown with "1-up" on them, rather than the now trademark green mushrooms. Also, what would become SMB2's Hawkmouth was a slightly scary tiki-like mask. World 7's vegetables were mean-looking, and the Mushroom Blocks were menacing masks.
Inverted with Phanto, who looked like a generic opera mask in this game. Strangely enough, Super Mario Advance's instruction manualnote And Super Mario Bros. 2's, for that matter would use the original DDP design.