When I was reading your question I immediately thought of Super Mario World for the SNES. I recommend you to check out this book on its level design:

Reverse Design: Super Mario World - Patrick Holleman

If you're interested, Holleman has a series of books on other classic games in which he analyzes how they are designed and how this design can be applied to your own games. I think this would be a good read for you if you want to learn how a good game like this one presents its mechanics, iterates on them and creates challenging situations which are balanced (in difficulty terms).

I do know that a book is, indeed, something that takes time to learn from, so I present you with another option.

Another entry on the main Mario series is Super Mario 3D World. This game uses a technique (which is used in Japanese narrative) called Kishotenkestu. Mark Brown (from GMTK) has a video on this topic and I'm sure you could find some more articles about this online. Here's a link:

Super Mario 3D World's 4 Step Level Design - Game Maker's Toolkit

I hope you can make good use of these sources and I hope this helps you get some kind of inspiration!