Action game level design is hard. If you want to hone your skills at designing action game levels, the problem is that first of all you have to make a good game, with good controls, interesting enemies, not to mention all the more basic code like collision, rendering, and of course the level editor (okay, so you could use an engine for a lot of that, but it's still a lot of work). Even once you have that, if your game isn't any good, that'll hinder any potential practice you might get from designing levels.
So I'm looking for 2d action games with level editors. In addition to reducing your work load and allowing you to focus on level design, having a complete game means that you can play the professionally-made levels first and have something to compare your work to.
Personally I'm thinking of sidescrolling action/platformers, but 2d action includes any 2d game that is primarily execution-based, ie reflexes and knowledge of the controls. So, Super Mario Bros. counts as 2d action in this instance.
My own examples are on the PC, but console games are fine too (although I think PC games usually have better level editors, maybe that's changing though).
PS: I hope this question is acceptable, even though there's obviously no single right answer. I noticed there's no "big-list" tag here, but I've seen questions like this on other SE sites, and it'll be plenty useful to future readers, which is part of the point of SE questions.