As for nitty gritty graphics, I highly recommend https://pikuma.com. They have free and paid courses, and go into a lot of the in-depth aspects you wouldn't get from using a web framework like I typically do.

As for game mechanics, Wikipedia is a surprisingly solid resource. I mean, it's expected that these things are covered, but the depth is amazing. Check out this page for example!

https://m.bulbapedia.bulbagarden.net/wiki/Damage

For in depth game mechanics, I'd check out Dragonfly Cave, as they cover so much of it, too!

https://www.dragonflycave.com/

To study the ROM, and how the 1st Gen games work, I recommend this article, which covers the mechanics of the bit level organization of the first games

https://www.smogon.com/smog/issue27/glitch

I would love to make a game that compiles down to almost nothing like GameFreak initially did.

Yeah! I've done it a few ways, mostly in React. I'm currently trying my hand at it in Solid.js, as I want to learn it, and Web Components.

As for graphics, I've been following along in this book, and absolutely love it. They have an online version. You use the author's bespoke engine, so it does abstract much of it, but it covers things from map generation to event buses!

https://pragprog.com/titles/hwrust/hands-on-rust/

You make a roguelike, but the concepts carry over. And it can compile to Web Assembly, so any work you do can be embedded and shared on the web.

I started one! You people inspired me!

https://mikercampbell.gitbook.io/gotta-code-them-all/