* HYPOTHETICAL!. How would you as a player or DM deal with this?

This is not happening in real life, I just want to know what you would do in this situation as a player or a DM?

lets say you are playing in a tournament with a magic being with the power to gaslight others and change their memories and can do one of two things

1. saying what one roll was when it was another roll (you roll a 19, but the other player keeps saying it was 11)

2. saying that you rolled multiple times when you only rolled once, just to goad you into rolling a bad roll or get more points. I.E accusing you of cheating when there was no cheating.

To balance it out, there are several things to account for. One, the magic being cannot gaslight you if you have physical proof of the event in question (a painting, a picture etc.) Two, if the being goads you into rolling again and you beat the being again, then the magic being has to offer you something in return. Furthermore, the magic being runs a company with several other beings that are getting sick of this creature's antics.

recently, you and the DM now have proof that this problematic being is cheating and was gaslighting everyone else on purpose. (you managed to goad HIM into a bad roll, and he's all out of options to cheat). How would you deal with this?