You answer my posts so its only fair to return the favor. This team is pretty good, especially for your first one. However I think you lack a little bit of immediate power. I like that you opted for two megas. As I said in the comments, if this is a VGC team you need protect. When I first started I thought it was stupid too, but I soon realized, the hard way, that it is very important. Also I plugged your team into Team Magma Team Builder and it checked out very nicely. Anyways I hope you like my answer.
Just a couple changes to your Kingdra:
Kingdra (M) @ Choice Specs
Ability:Sniper
EVs: 248 HP / 252 SpA / 8 SpD
Modest Nature
- Icy Wind
- Draco Meteor
- Muddy Water/Surf
- Signal Beam/Hydro Pump
Icy Wind acts as speed control and hits both opponents.
Muddy Water and Surf also hit both opponents, you can either go for slightly more power and accuracy or have the nice chance to lower both opponents accuracy.
Signal Beam for coverage or Hydro Pump for sheer power your choice.
Mawile-Mega (F) @ Mawilite
Ability: Huge Power
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Iron Head
- Play Rough
- Sucker Punch
- Pain Split
I think Mawile looks perfect. I have never used one before but that is the set I would use.
Breloom (M) @ Focus Sash
Ability: Technician
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Spore
- Bullet Seed
- Mach Punch
- Protect
Breloom also looks really good, I would use the damage calculator to make a more custom EV set but it really isn't required. Protect is almost mandatory in VGC, makes them think about double targeting your Pokemon.
Chandelure (M) @ Choice Scarf
Ability: Flash Fire
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
- Heat Wave
- Shadow Ball
- Protect
- Trick
Very good Chandelure, nice old trick...no pun intended haha. But again one change. Btw do you know if shadow tag Chandelure is banned because if not use, the shadow tag chandelure as it would go very nicely with trick and giving them the choice scarf. I found one source that said it was and another that said it was not.
When you already have the choice scarf boost, timid is not necessary, go with modest for more power. Also heat wave hits both opposing Pokemon and is over all a great move. Also you already have grass moves with Breloom and Thundurus, energy ball is not needed, however protect is always useful.
Kangaskhan-Mega (F) @ Kangaskhanite
Ability: Parental Bond
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Fake Out
- Power-up-Punch
- Sucker Punch
- Double-edge
This is a very good Kangaskhan, fairly standard. However I'm going to make it even more standard.
Earthquake is a good move, but it would damage all of your allies except for Thundurus, so I went for Power-up-Punch instead. An incredible move with parental bond. I also switched return with double-edge as I figured "why not go for maximum power?" with a base power of 270 when STAB is included it will take a chunk out of any Pokemon, also it is a great dying move. For this one, that is the EV spread that you want, so you can overcome or at least speed tie, with the large base 100 speed group.
Thundurus (M) @ Life Orb
Ability: Prankster
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Protect
- Taunt
- Thunderbolt
- Grass Knot
Again this Pokemon looks pretty good. I dont see a very important reason to chose Volt Switch over Thunderbolt, might as well get the extra damage, especially with the life orb. I think grass knot is okay.
Thats the best I could come up with, but overall great job.