Okay, this will be a long question, so bear with me.
I'm currently working on a start screen for my 2D platformer. I'm thinking to make it similar to one of the Mario games. I could have just used a background, but I want to do something else.
The start screen I want looks like this:

It's Super Mario Bros. Wii with Mario, Luigi, and the Toads running with the camera following them. It's pretty simple, yeah?
Right now, I have created the Control Node, all that left is the background.


Now let's get to the problems.
Should I make the background under the Control Node or should I make a scene? The way I see it, I think it's better to make a scene instead of making it under the Control Node. Not to mention, the main framework* I'm using. However, I'm listening to your suggestion.
How do you generate the ground? Basically, as the player character run, the ground will generate. I don't think tilemap is the best option here. So maybe something like a StaticBody2D.
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*The Main Framework

Main (The entry point and the brain.)
-Level (The current level)
-InterfaceLayer (The layer of the interface)
--HUD