To add onto what @Robotnik said, even if you can't earn robux in game (which it seems like you can't, but nevertheless) it's still on-topic to ask if there is a way to get them at all, and it is not restricted to having to be obtainable without actually paying.
The (original) question actually posed two separate questions:
In the title: "Why do I turn into super Mario instead of fire Mario?", and
In the body: "Is this a bug?"
We can (and have) answered the former. Experts in Super Mario have decompiled the game code and figured out the 'Why'. This showcases the core what our site is about - ...
I believe that the moderator that closed the question believed it to be under the following prohibited question category:
Speculations on future of the industry, upcoming (but unreleased) games or content, and developer intent on mechanics and narrative
The way I see it, a question that asks "Why is this feature the way it is?" and that can be ...