Samus does have the morph-ball ability, so you are right that she turns into a ball. Theres a very famous Metroid meme titled "Why can't metroid crawl" that I was making a reference to. Sorry if i ended up confusing you with that.
You should look it up! In fact I'll link to it right here! Just a cool in-joke in gaming, and it also just worked in a compare-contrast sense for that comment.
Also I don't know why I didn't realize that you had said this in your comment on 4/19 but Mario does have the ability to crouch in his 2D side-scroller titles. I can say with certainty that it's a mechanic in Super Mario Bros 3, and now that I'm thinking on it its definitely in 2 as well, but I'm almost certain that it was even in the original Super Mario Bros. Maybe I misunderstand what you mean but in 2 and 3 it's a pretty important mechanic for gameplay, specifically for 3 because of the flutes.
Ok thanks for that in-joke thing u mentioned. Anyways, about the crouching that I mentioned in my previous reply, what I meant in there is that the nuinui quest game doesn't have crouching, not even a crouch similar to that of mario in his 2d platformers, where I can't move when crouching but can crouch jump to move while crouching.