Mega zorark would be awesome. Period. I would give it the ability illusion but if it mega evolves your obviously going to know its a Zorark. Instead it gets a new ability (made up) called concealment. This ability makes it to where only the user of Mega Zorark can see its Hp. to all others, it will always look as if its at full health. It will also hide status conditions and what moves it uses from others- they'll receive the damage and/or other effects but never know what move it was. Zorark gets a boost to all of its stats and now has sharp claws, blood red eyes, and is bigger and more aggressive looking. It also is surrounded by a dark fog. This would be a great mega for players who can predict their opponents moves, and it would be very fun to play with.
Stat boosts:
10 sp defense
20 defense
20 speed
30 attack
20 sp attack