As I've pointed out plenty of times, Mega Durant is just stupid. There's no flavorful reason whatsoever for it to have Will o Wisp or Flare Blitz. Fire Absorb would fit much better if we absolutely need it to be Fire-immune.
In any case, from before:
Dragonite should be changed, given Storm Force is an absurd ability (Sand Force's boost to Rock, Steel, and Ground makes sense given the three's direct relation to sand; rain improving Electric and Flying makes sense thanks to Thunder and Hurricane, but Dragon? Makes no sense whatsoever, outside of wanting to make the ability fit with Dragonite).
Marowak: 105 Huge Power is already known to be bannably powerful (thanks Mega Mawile), and despite a worse defensive typing, Mega Marowak is even bulkier in terms of stats. Moreover it's got actual STAB on that Sucker Punch, STAB Pursuit to trap, STAB Earthquake for incredible power, and far better coverage than Mawile in the elemental punches and good Rock options to boot. Yes, this is a meta full of megas, but Mega Marowak is too strong even for that.
And also:
Porygon-Z: 85/90/90 defenses gives it enough bulk to use Agility to boost that 80 Speed. That's all it takes for it to use Protean, its incredibly diverse movepool, and its 185 Special Attack to kill absolutely everything.
In general, we need to look over any mon that gets new boosting moves or recovery moves, as in general they make plenty of non-mega pokemon way more viable. Slack Off Nidoqueen, Roost Empoleon, Coil Druddigon, Recover Claydol, Calm Mind(/Moonblast) Togekiss, Nasty Plot Roserade, Bulk Up Honchkrow, Agility Exploud, Coil Scolipede, Recover Qwilfish, and the aforementioned Recover Lanturn make their standard forms far more viable, which ruins the whole point of this project.