Perhaps we should set some rules about fan-made Mega Evolutions, because you all are breaking the metagame with your creations
You do not need to adhere to the rules by word, but I think they are nice guidelines for more "healthy" creations.
1) Do not abuse the minus (-) in your creations. Yes it was cool when Beedrill lost all SpA to get a ridiculous boost to its Atk and Spe (not to mention adaptability) but that was made because Beedrill was never going to be used in any tier and was garbage in general. Other megas, when they lose a stat, it's most times speed, and it's a small loss like -10 to Garchomp and Heracross, that makes the player think twice before using them, in their whole OP-ness. While I understand that you wish to make your pokemon the bestest in its aspect, it's an overkill to decrease a stat it does not use anyway, just to boost another you feel should be OP. We do not want out pokemon to go straight to ubers now, do we?
2) Stay to the concept. This is not necessarily a rule followed by canon megas with Zard X being the prime example, but the main idea behind a mega evolution is to make it better at what it already does. Turning a slow defensive pokemon into the ultimate revenge killer does not seem the best course of action. I'm not saying we should not provide the megas with versatility (we should) but not turn it into something it never wanted to be.
3) Try to choose pokemon that are already underused or forgotten. That's why megas came in existence in the first place! Yes, they boosted the fan-favorite pokemon like Scizor, Mewtwo, Lucario, Gen1 starters and Audino Gyarados, but they also made sure to bring forth some pokemon we would never even consider using before, like Manectric, Sceptile, Banette, Abomasnow and most notably Beedrill and Pidgeot. I'm not saying they always did a good job but the main idea is what matters most.
4) Explain how what you give is us different. Before creating a fan-mega, make sure you have a theme in mind, and aim to give us a pokemon that can not only improve its own role, if any, but also be able to stand out when mixed with others. In other words, why is your mega different or unique, and why should I use it? That of course better avoid ridiculous stat boosts or abilities that come out of nowhere. It's not an easy job, but you won't need scientific theories or clinical trials approved by Medline to create a mega. Find out what it is, how it is different, and give it to us. Frankly speaking, nobody wants to see a CharizardY.v2 or an overpowered Lucario-ish copy. Following up that thought, the best way to determine what boosts to give is to visualize what roles you want it to fill in a team. For example, M-Zard-X is a setup physical sweeper, M-Slowbro is a mixed wall, M-Gardevoir a special Wallbreaker, and M-Banette a... ok I don't know what this one is either.
Cheers.