Are we aloud a bIg magnet at the back of our bot

Are you trolling? Unless it serves a purely “non-functional purely aesthetic” purpose, no.

This is a joke, right?

No. You’re going to attach to the field and other robots.

Hmm… Unless the magnet is really weak, no. There is no way a magnet is purely aesthetic and non-functional when it comes to electronics, metal, etc. interacting.

Sry to anger you but I was just wondering it was a fridge magnet

When you said a “big magnet” it seemed like you meant a large magnet like this:

A fridge magnet would most likely be alright if it’s only for aesthetic reasons but judges might have a problem with it because of the potential to interfere with electronics.

Personally I would just put it on and if the inspectors call you out on it, it only takes a second to take off.

I agree with drdaniefc. (I was also under the impression that was the kind of magnet you were talking about, I suppose more like this, but what’s the difference). You shouldn’t have any issues with a fridge-type magnet.