The Mawile set is....strange. You have two moves there for the sole purpose of gaining extra bulk, one of which is Redundant with the other (Both Iron defense and Stockpile increase Defense). To be frank, there are better baton passers, the answer above me mentioned Scolipede, who is definitely a good option for passing either bulk or attack (Has access to both Swords dance and Iron Defense). Another Baton pass possibility would be a Venomoth with Quiver Dance, increasing your Sp. Def (As well as Sp. Attack/Speed!)
This mega Gengar is a huge Gimmick. If you're okay with playing this style I obviously can't stop you, but few people really respect this form of play. The build itself is....odd. really you're putting two whole pokemon (Mawile is made the way it is to pass additional bulk to Gengar) into making this one strategy work which is a real waste. To be honest, you could easily use both pokemon still, but switch the mega stone. Mega Mawile is a serious threat that can destroy lives. It gets access to the almighty sucker punch, as well as Swords dance and Play rough. Gengar could be brought back to a regular Special Attacking Gengar with a Timid Nature/Life orb.
Mandibuzz is fantastic and I really need to breed one for myself.
Azumarill is a very awesome choice for an OU team. The set you have is ALMOST perfect. Aqua Ring, while attractive on paper, is a rather costly move to run. You spend an entire turn bringing the effect up, allowing your opponent to either Damage you or switch into something that can kill you with a super effective hit. My Suggested Set would be one of two: Choice Band or Belly Drum. Choice Band Runs Waterfall/Aqua Jet/Super Power/Play Rough. It Sacrifices Move switching for a (Very noticeable) attack boost. With this set, it is important that you pay attention to your opponents team and think of what they may want to switch in against you. Belly Drum is gone over in the other answer given.
For electivire, I 100% recommend a Jolly Nature. Keep the Motor Drive (You can switch him into any predicted electric attacks and possibly sweep the enemy team afterwards), but your Moveset is lacking. Sure it has nothing that resists it, but Check this out. Your Set: 203 Normal Effect, 571 Super. New Set: Wild Charge/Earthquake/Ice punch/Cross Chop : 1 No effect (Shedinja), 168 Normal Effect, 605 Super! Unless you really are scared of Shedinja, Cross Chop really is the way to go, allowing you to have even better coverage, while also being able to have a Jolly Nature and invest fully into your Attack and Speed Stats. For an item, I would recommend Either an Air Balloon (Switch in on Ground attacks and Kill with Ice punch! Haha!) or a Life orb (If you can get another one, doubles of items in Singles ARE allowed unless you're playing battle-spot).
EDIT: Electivire also has access to Fire punch, so if you're really set on running a Fire move over Cross Chop, I would recommend Fire Punch over Flamethrower. It uses your (Much higher) Physical Attack, while also allowing you to Invest more economically as I mentioned before.
I personally would probably use Dragon Pulse over Draco Meteor due to you not really having any /real/ walls to switch into after lowering your special attack. From my experience, Draco Meteor is usually run on the Focus Energy Kingdra Set, as it can ignore the special attack drops with its crits. What type of Hidden power are you running? I'm not really sure what type would benefit Kingdra (Fire maybe?), but Flash Cannon may be a viable choice for you to run instead, as it hits Fairies for x2 damage. I would also recommend switching your Ice beam out for a Water type move, Which you have quite a few options for: Scald, Surf, or Hydro Pump. Surf is Probably the best choice in terms of pure damage/Accuracy, Scald loses some power to give a burn chance, and Hydro pump goes full power while only having 80% accuracy. Choosing one of these would hit your Super effective numbers a bit, but also take down the number of pokemon that can force you to switch out due to you having nothing to super effectively hit them (Only 3 Not Very Effective with Water/Dragon/Steel). Also it gives you both your STABs, allowing you do deal out a good deal more damage overall.
