What Is a Mega Charizard Y

Mega Charizard Y is a Mega Tier Raid Boss, with a Raid Boss CP of 53873 and a dual Fire / Flying typing.

Is Mega dragonite real?

You are indeed correct. This is why it is one of the few fully evolved Pokémon that will never get a mega-evolution. It is joined by Meganium, which would become Mega-Meganium, and Yanmega, which in English becomes Mega Yanmega, but more amusingly in Japanese becomes Mega Megayanma.