Sorry to ask a lot of q's but I dont play ubers often so i wouldnt know but hows mewtwo in the oras metagame? It was always a "strong" pick but i dont see it that often, in any form. Is it because neither the mega nor base form is particularly good at one thing? Or msabaleye ruining mew-ys sig set? What are other reasons?
If you play on the ladder as you probably do, I guess that you see less Mewtwos because of how Salamence is good now, as you probably know you can't run two megas in one team so Mewtwo's usage dropped a bit, even Diancie was another good mega that ORAS brought, even if of course it isn't as good as Mence is. However, both regular Mewtwo and Mega Mewtwo Y are really viable in Ubers (as you can see in the viability ranking, they are both A+, which means they are very good). Definitely the introduction of Mega Sableye didn't make them worse imo, as it hasn't a big impact in tier, but I guess that the introduction of new megas (especially of Mega Mence as I said before), made things a bit worse for it, even if it still remains a top tier mons. Regarding Mega Mewtwo X, it's viable (A- rank in the viability ranking), but it isn't as good as the other Mewtwo. I also think that it got a bit worse in ORAS, in fact Lati Twins are top tier threats now that we can use Soul Dew, and Ho-Oh also became more common now that we have the chance to have better Defog users in the tier in Latias and Latios. All these 3 mons can check Mega Mewtwo X well. Finally, obv the introduction of Mega Salamence made things worse for Mega Mewtwo X, as it's able to lower its Attack before mega evolving, and then can slayer it with its strong flying STAB. It has the niche to be one of the best answer to DarkCeus though, which is becoming more common now because it can check Lati twins well. Hope I helped somewhat.