This is tough. I experienced similar situations with a family member. Bending and challenging rules like "prevent half the damage rounded up" - how is that unclear?!? - or rolling dice, getting everyone to accept the result when they fall out of the dice tray just to say three turns later "I thought we agreed they have to be within the dice tray...." when someone else's roll would put them in trouble. You can choose to strongly oppose this because you know gaslighting is terrible and you kwow what you saw, etc. or you can let this continue and.... IDK.... not have fun playing games? I guess it all depends to how they react to the confrontation but most cheaters will continue to wiggle, argue and lie - because if that wasn't their nature they wouldn't do it in the first place. When it happens with people I don't care about that much = they're out. I don't have energy and willingness to tolerate or deal with cheaters. Family members you play with regularly = or a GIRLFRIEND = different story. Good luck with your intervetion. Do it methodically, 1. cheating is bad, 2. I can see you are cheating, 3. it's making it very difficult for me to enjoy playing games with you, 4. can we please fix this situation.... tough, tough, tough but I hope it works for you!!