>>55933189>Multiple MewtwosMewtwo is a clone. As long as sufficient genetic material is provided and an advanced enough facility with capable enough scientists, there is logically no limit to the amount that could exist as all they would need to do is repeat an already proven process.
>Mega StonesThey're a result of evolution stones being irratiated by the energy of Yveltal and Xerneas upon the Ultimate Weapon. Hypothetically, as long as more can come into existence due to ambient energy in the region whilst Yveltal/Xerneas are alive or something, there's no reason why a Mega Mewtwo stone couldn't come into existence at a later point, though the real reason is obviously just fanservice.
Mega Stones appear in ORAS after Primal Reversion occurs in the box legendary so for all we know, the energy used for Primal Reversion or perhaps Infinity Energy can cause the necessary irradiation. If so, someone could possibly exploit this and intentionally irradiate stones to create them for Mewtwo.
But again. We all know it's because Mewtwo is popular and needs to be wanked appropriately.