Yu-Gi-Oh! » Rulings Q&A

https://www.duelingbook.com/replay?id=384240-73454476

No, he has no effects. He is trying to add effects to Normal monsters.

Pretty sure "cheating" is a stretch here.

Their username checks out, they were trolling you...in an unrated match. (That is what it looked like to me)

So there's no reason to ban a cheater in non ranked.

I agree. Normal Monsters do not have effects unless a specific card or game mechanic grants them one. Read more by https://geometryslope.com

I check the log and you where in unrated custom room, maybe your opponent thought custom room mean custom rules, and that is not what it meant to be in a custom room, so you are more likely to found trolling player like that in custom room, and the reason why he was behaving like that was probebly because he is salty that all of his opponent in custom have broken effect from custom made card. So he just end-up not caring anymore