what is mega rayquaza weak to

Mega Rayquaza is a Dragon/Flying-type Pokemon, which makes it weak against Dragon, Fairy, Ice, and Rock-type attacks. It is double-weak against Ice. According to a Reddit post, Dragon and Fairy types are the only types that can exploit its weaknesses. Based on the information from Pokebattler, the best counters for Mega Rayquaza in Pokemon Go are Shadow Mamoswine, Mega Gardevoir, Shadow Mewtwo, Mamoswine, Mega Glalie, and Mega Abomasnow.