This new version was throughly tested by Chris and many glitches were taken out thanks to jiangzhengwenjzw, now most glitches from all previous versions should be gone. Also, there're some new additions:
A new event was added, now you need to capture Mewtwo before facing Rayquaza, and once Rayquaza is captured, the new event will unlock a new form of Mewtwo.
The music was fixed a little bit more.
PSS Split system was redone, now the category icon is shown.
Exp Share system was redone thanks to jiangzhengwenjzw's help, now it works exactly the same as how it should be in generation 6, and it can be turned on/off through a key item.
The movepool of all fully evolved Pokemon was redone, several new moves were added and some old moves were made to be more useful, like the HMs and so on.
The cries of Pokemon were corrected, also, the sprites of the Pokemon from the later generation were adjusted a bit.
It's possible to fly to all towns, this wouldn't be possible without jiangzhengwenjzw's help.
Also, with jiangzhengwenjzw's help, there are features like making a Pokemon shiny were added.
So, this new version should be way more stable than the previous ones. However, the old save file will not be compatiable with the new version, because the whole save data structure was greatly changed.
Download link of the updated Beta 5.7(The save file from the versions before Beta 5.7 won't be compatiable with this):
https://www.mediafire.com/file/ecx654uu0azmnv4/Mega+Power+Beta+5.7+Fixed.zip/file