What is the deal with the tube that runs out of the backplate? What is it's purpose? Is it ROAR legal to do that? If not, do I need to replace the backplate or just over it?

The tube that runs from the back of engine is the boost chamber, it is supposed to make the engine rev harder i think. As far as i kno they are roar legal

I am not sure though but I think it take unburnt fuel from the bottom of the block and puts it back into the carb.

While we are on the topic of Fantoms could someone please answer one of my questions?

What are Fantom's engines based off of?

What do you mean? Like they are based off of another engine?

fantom engines are made by rossi (not novarossi, but rossi the company that makes the pixi black engines)

Thank you

Team-RTR You could be wrong...
I think Fantom engines not made by rossi engine,
Fantom's engines based off of Japan manufacture, like EPIC,PEAK,and some Team Orion engines(.18). All made by the same manufacture in Japan...

epic is also made by rossi

I do not know where you are getting this but Epic, Peak and Fanom engines are as close to being made by Rossi as apple pie being invented by in Japan.