I see a bunch of collection item minions in the Galaxan Wastelands, but I've never seen a Sweetshroom. Is there a reason for that?

I'm pretty sure they're randomized. I think it's just luck of the draw as to which minions show up. As far as I know, none of them are off limits.

You know, it's true that a lot of more recent minions do not seem to show up there