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Mega Quagsire
Type:
Water/
Ground
Ability: Marshland Lord (Sets Water Sport and Mud Sport upon switch-ins)
Stats:
HP: 95
Atk: 110 (+25)
Def: 125 (+40)
SpA: 100 (+35)
SpD: 65 (+0)
Spe: 35 (+0)
New moves: Flip Turn
It's hard to pull Mega Quagsire off, few abilities are able to fit the flavor of Quagsire as well as Unaware while allowing it to differentiate itself from its base form, but Marshland Lord does both while putting into work the effect of 2 moves with huge wasted potential.
Quagsire now creates its own swamps to live in AND make a living out of it, after all, Quagsire is a landlord in the Mystery Dungeons series :)
Competitive Design
Quagsire has a huge twist in its role as a mega, now it is a defensive pivot meant to support its teammates through its ability, able to reduce the damage of Fire and Electric type moves to 1/3, allowing teammates such as Gliscor, Scizor, Amoonguss to check the likes of Simisear-Mega, Zapdos, Heliolisk-Mega, Volcanion, Rotom-Heat/Wash, and others, much more efficiently, and while the ability might sound broken, it's worth noting that Quagsire itself can't switch safely into most of the mons listed previously, thanks to its low SpD, which allows it to still be threatened by most strong special attackers, forcing you to play very carefully to keep it alive. It's very important pointing that although Marshland Lord brings many benefits to Quagsire and any team that chooses to run it, it also has its disadvantages, Marshland Lordakes your teambuilding process much more restrictive, after all, your team is also affected by it, it discourages you to run the likes of Zapdos and Rotom-Heat, which would make up for great partners for Quagsire-Mega, gives Volcanion a hard time dealing with grass types like Amoonguss, as they can switch in much more safely, and overall makes it harder for any mon that relies on Fire or Electric coverage to deal with Scizor, Slowbro, Ferrothorn, and many others dominant mons of the metagame.
EDIT What differentiates Quagsire from other potential users is the fact that Quagsire does not benefit from the ability itself, it already resists those moves naturally and its SpD is way too low for it to sponge any secondary stab or even coverage the mons it helps keep in check through its ability; it's also important noting that although the Flip Turn addition might look like overkill, Marshland Lord's effect will only last 3 turns for its partners, as it takes 1 turn for Quagsire to switch into the field, and 1 to switch out, outside of situations where it comes in as the lead or to replace a previously killed mon, where Marshland Lord only lasts for 4 turns, but that'd also be presuming that you're not using any move other than Flip Turn, any Mon able to force Quagsire to Recover or attack too often can neutralize its ability almost completely, which is a weakness far easier to exploit thanks to its mediocre SpD, which makes both effects of the ability not only needed, but also balanced.
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:
:
Mega Jumpluff, 
Mega Rhyperior and 
Mega Florges are open, effective immediately!
