I have rounded up a couple videos that discuss basic design principles behind the best Mario levels. Whether you want to improve your own level design or just see what Miyamoto and Hayashida had as guiding inspiration, you may want to check it out!
Hey guys, I've been playing your levels and they're amazing! Is it ok if I post completion videos here? I plan to finish them all someday and record them on video!
Unfortunately, I can't share mine as I don't have any good levels yet, so I will just share my favorite levels: Skyzo by PangaeaPanga - Everybody knows this level. This is an entry level Kaizo, if you're new to Super Mario Maker and you want some really challenge right off the bat, then this one is the best to play Koopa Surprise by MrSuhSpence (Player 4 of WRTP) - Simple level design, a few challenging but good platforming, no clusters. Overall a good level. This is a level created by WRTP, a famous YouTube channel. Simple Bros. 1-1 by [SrL]dram5 - Overall a very easy level. Very good level design and very fun to play with. This is created by master speedrunner dram55. Use your noggin! by [SrL]dram5 - Another level by dram55, but this one's a puzzle level where you use your head to get past obstacles. Very good puzzle level and very satisfying to finish.
I have a lot more to share, but these are the best. Enjoy!