There are no mega evolutions before Pokemon X and Y
No! Of course not!
No
Aerodactyl can only Mega Evolve into Mega Aerodactyl. Permanently, Aerodactyl cannot evolve any further.
ditto does not evolve on firered or leafgreen
Xerneas does not have a Mega Evolution.
No it is not possible but you can evolve it on Pokemon Diamond and Pearl if you wanted.
nothing
Mewtwo is the ultimate Psychic type legendary Pokemon. It was introduced in the first generation and does not evolve into any other Pokemon, although as of the sixth generation it can mega evolve into Mega Mewtwo X or Mega Mewtwo Y.
Aerodactyl can only Mega Evolve into Mega Aerodactyl. Permanently, Aerodactyl cannot evolve any further.
ditto does not evolve on firered or leafgreen
You cannot evolve Murkrow in FireRed.
Rhydon is not able to evolve in FireRed.
Electabuzz is not able to evolve in FireRed.
THEY DONT EVOLVE
Have it hold the Sceptilite, then press "Mega Evolution" during a battle to Mega Evolve it.
Pinser in Pokemon does not evolve into any other creature. Pinser does evolve into a Mega Pokemon using the Mega Stone at any level.
Xerneas does not have a Mega Evolution.
You evolve it at level 20
trade it then it will evolve