Greninja
Choice Scarf Greninja is not the best idea, but it is a good idea. However, listen up: you will need two choice items for this team, and none of them will go to Greninja. You will want Choice Band and Choice Scarf for Talonflame and Excadrill, respectively. Greninja is better going with a Life Orb set because of your team. So let's go:
Greninja @ Life Orb:
Trait: Protean
EVs: 252 SAtk / 252 Speed / 4 Atk
Hasty Nature
- U-Turn
- Surf
- Dark Pulse
- Ice Beam
The best set for Greninja. Its goal is to decimate HP in order to brutally hurt everything in your way, with STAB and Life Orb boost, courtesy of Protean. However, if you lead with Greninja, go for:
Greninja @ Focus Sash:
Trait: Protean
EVs: 252 HP / 252 Speed / 4 SAtk
Timid Nature
- Spikes
- Taunt
- Scald
- U-Turn
The goal is to Taunt Hazard Leads, and then set up Spikes after they are rendered useless. This set is magic against Stall-based teams, as you will see Greninja last for more time than evaluated. This is the proof that Hyper Offense can still beat Stall. But this set is not Hyper Offense, so use it only if you prefer a more balanced team, as Hyper Offense have problems against Stall.
Haxorus
Respecting your choice, go for Haban Berry / Yache Berry Double Dance set, as this is frankly deadly:
Haxorus @ Haban Berry:
Trait: Mold Breaker
EVs: 172 Atk / 84 HP / 252 Speed
Jolly Nature
- Swords Dance
- Dragon Dance
- Outrage
- Superpower
This setup set likes the support Greninja for better sweeping. Once you danced twice, your attack is sky-high and your speed reaches 400 and more, which is ideal for sweeping. Who would like an Outrage served at a tumultuous-high attack ? Frankly, if Outrage is not enough, you have Superpower. And Superpower > Earthquake because otherwise, Skarmory totally walls you and force you out of the way.
If you prefer a more offensive set, then go for all-out attacker with Life Orb, and
- Dragon Claw / Earthquake
- Outrage
- Superpower
- Rock Slide
and you are fine.
Excadrill
Try Scarf Excadrill, because it rocks. Seriously, 412 Speed and 405 Attack is so high that many Pokémon fears 2HKO or OHKO. You can check it by doing calcs, because I am lazy to show you.
Excadrill @ Choice Scarf:
Trait: Mold Breaker
EVs: 252 Atk / 252 Speed / 4 HP
Adamant Nature
- Earthquake
- Rock Slide
- Iron Head
- Rapid Spin
Excadrill is simply a mighty beast that one should avoid facing.
Alakazam
I love your Alakazam name, but sadly, Modest is not the best nature to go with. Mega-Alakazam is okay, though there are better ones. You need a special sweeper, so why not ?
Mega-Alakazam @ Alakazite:
Trait: Magic Guard -> Trace
EVs: 252 SAtk / 252 Speed / 4 SDef
Timid Nature
- Psyshock
- Focus Blast
- Shadow Ball
- Energy Ball / Dazzling Gleam
The three first moves are self-explanatory, as together, they cover very well. The last slot is whether you have problem dealing with Dragons or Ground, Rock and Water. I'd go with the former. And forget Calm Mind, its bulk is little at best, so you won't be setting up anything. Try not Mega-Evolving since the first hit; profit of Magic Guard, because it is an excellent ability. When needed, Mega-Evolve.
Talonflame
Talonflame @ Choice Band:
Trait: Flame Body Gale Wing
EVs: 252 Atk / 252 Speed / 4 SDef
Modest sorry. I mean Adamant Nature.
- Flare Blitz
- Brave Bird
- U-turn
- Me First
The three first moves are the main ones, as you boast dual STAB and scouting move, and I am not going to bother explaining each move in details. Me First is a gimmick à la Ditto, but with a twist of usefulness: No Dragon likes to be outraged, and Talonflame will show them why.
Ferrothorn
If you will use Greninja's support set, then change it for Infernape. If not, then keep it.
Infernape @ Focus Sash:
Trait: Blaze
EVs: 252 SAtk / 252 Speed / 4 SDef
Timid Nature
- Fire Blast
- Focus Blast
- Stealth Rock
- Grass Knot
The two first moves are dual STAB, and use special Infernape because Alakazam is never enough with its paper bulk. Stealth Rock can be used for ... you know, yes ? Helping the sweep. Grass Knot should deal with obese Pokémon like Mamoswine or Donphan.
I hope this helps.
~ Sincerely yours, Blitz of Justice.