My Friends think Mario Odyssey is a Bad Game...

What should I do or say?

I kinda dont like IT because theres Mecha Wigglet but the best thing is that theres a Mario 64 outfit

Nothing.
Media-be it film, audio, or otherwise-is a subjective field. One person may think a piece of media is a masterpiece, another may not. It's all up to personal opinion really, even if something is widely acclaimed like Mario Odyssey.
If anything, the more universal praise a game gets at launch, the more likely you are to see people who will crap on it just because they disagree with the mass opinion later down the line.
Many games from the 5th or 6th generation of gaming that "haven't aged well" have fallen into that trend, most notably Super Mario 64 and Sonic Adventure 2

It’s a great game. You’ll probably want to play it secretly before they kill you like my friends brother

Whats bad about that? I dont like it either