Why is heat wave listed for ninetales? Fire Blast is much stronger while only losing slightly out on accuracy. Also, change the EVs to put more on speed. Possibly Timid would work better.
You have sun, but you don't have any pokemon that can benefit from it, other than claydol who perhaps has one weakness nullified. Other than that, you double the effectiveness of fire on half of your team that is weak to it.
Never, ever, ever, have a neutral nature. There's never a pokemon that performs every role equally, even base 100's all around such as mew. If the pokemon is a physical attacker, make it adamant. SPecial attacker, modest. It's at least better than docile.
Also, the items seem to be randomly placed. Weavile, for instance, does not make a good user of the Leftovers. Weaviles do not last long +6% or no, meaning that leftovers could be left alone instead of a more helpful item, say Life Orb, which allows more power at the expense of some bulk, which is borderline irrelevant as Weav's paper defenses mean any neutral hit is a KO anyways.
MEganium won't be able to take down foes with unsuspected moves because her low offenses mean she's really not gonna hit anything for the KO. A good opponent will simply switch in a bulky sweeper and set up, possibly defeating your whole team.
Your team could use a bulky water instead of meganium, perhaps, which would alleviate your fire/ice vulnerability and create a FGW core.