I recently found 2 bugs with pertaining to Mega Charizard.
Bug #1 Mega Charizard Y not having flying animations. This Bug shows Mega Charizard Y standing still while moving in the air.
Bug #2 Mega Charizard Y not dropping the correct Mega Stone. After beating said Mega Charizard Y I received a Charizardite X Stone instead of the Charizardite Y Stone.
Sorry if that there are 2 bugs but considering that they are from the same major issue I thought that it would be wise (On my part) to clump them together since they have to do with a Mega Charizard.