After some thought and consideration, I have decided to rule the following:
Megas are not allowed.
Z Crystals are allowed.
Part of the reasoning for banning Megas goes back to the forms. In the case of this they were introduced in Generation 6, and with the exception of Mega Diancie there are no Mega Evolutions. I may re-consider Mega Diancie since it was within Kalos, but in the meantime the remainder of the Megas remain banned.
As far as Z Crystals - they are an item, and a big "appeal" to this generation's release. I decided to allow these to give a little spice to games.
If you want to drop, I completely understand. All you have to do is delete your post. Still, I would like to encourage and welcome everyone to still continue participating.
This will be edited in the OP to reflect the changes.