This team won't require many changes. It's fundamentally good, and on,y has a few worries. I'll try to keep in mind that this is for WiFi, so you have to catch/breed/trade for any Pokémon on the team. Changes are in bold.
Ready… Set… Rate!
Sceptile
Sceptile@ Focus Sash
Ability: Overgrow/Unburden
EVs: 252 Atk / 252 Spe / 4 Def
- Leaf Blade
- Swords Dance
- Earthquake
- Drain Punch/Rock Slide
I like the Physical approach to Sceptile, he has such an overlooked Physical movepool. Anyways, I know you probably don't have access to Unburden, but if you do then definitely choose that over Overgrow. The Speed boost may just be the deciding factor in Sceptile's KO of the opponent or the opponent's KO of Sceptile. The only other change I made was to Acrobatics; it wasn't covering much. Instead, try replaxing it with either Drain Punch for recovery or Rock Slide to revenge-kill Talonflame, whom your team suffers from.
Latias
Latias@ Life Orb
Ability: Levitate
EVs: 232 SpA / 252 Spe / 24 HP
- Roost
- Dragon Pulse
- Psyshock
- Thunderbolt
My changes to Latias are simple: less bulk, more sweep. EVs were altered to better suit that playstyle, and even without the HP EVs Latias still has plenty of natural bulk. No moveset changes.
Garchomp
Garchomp@ Choice Scarf
Ability: Sand Veil
EVs: 252 Spe / 252 Atk / 4 HP
Jolly/Naïve Nature
- Dragon Claw
- Earthquake
- Stone Edge
- Iron Head/Fire Blast
Scarfchomp is a beast. With an already crazy base 102 Speed as well as devastating STABs, this 'Mon is a force to be reckoned with (or 'wreckoned with'). My suggestion is to run a mixed set, replacing Iron Head with Fire Blast. However, since most Fairies have pitiful Defence, Iron Head should work just fine.
Sylveon
Sylveon@ Pixie Plate
Ability: Pixilate
EVs: 248 HP / 8 SpA / 252 SDef
- Hyper Voice
- Wish
- Protect
- Hidden Power [Ground]/Hidden Power [Fire]/Toxic
I had to choose between Sylveon and Vaporeon for who got Leftovers, and I thought that Vaporeon needed it more. Other than that, the only thing that needs changing is the moveset. Hyper Voice > Moonblast > Echoed Voice, once factoring STAB and Pixilaite boost. Also, if your Sylveon's Hidden Power is Ground or Fire, choose that to take care of nasty Steels and Ice-types, respectively. If you have neither Hidden Power then choose Toxic, as status is always a nice thing to have.
Vaporeon
Vaporeon@ Leftovers
Ability: Water Absorb
EVs: 252 HP / 252 SpA / 4 SDef
Bold Nature
- Ice Beam
- Scald
- Wish
- Protect
Two Wish users? Alright. Vaporeon gets Lefties for obvious reasons. The only change here is Scald > Surf for the Burn chance. A Bold nature makes Vaporeon more bulky.
Mega Blaziken
Blaziken@ Blazikenite
Ability: Blaze > Speed Boost
EVs: 252 Atk / 252 Spe / 4 Def
Jolly/Adamant Nature
- Flare Blitz
- High Jump Kick
- Protect
- Earthquake/Thunder Punch/Brave Bird
You asked if there was a suitable replacement for Arcanine, and here it is. An absolute monster in any battle format, Mega Blaziken brings some oomph to your team. Protect on the first turn when you Mega Evolve to nab the Speed Boost, then wreck everything with Flare Blitz and HJK. This is where your two Wish passers come in handy, as Mega Blaziken accumulates a lot of recoil. In the final slot, Earthquake provides additional coverage, Thunder Punch covers Water (but Vaporeon is the best counter for those) and Flying, but lacks power. Brave Bird is for if you want to go full suicide spam, but don't expect to last very long. If you're having trouble getting a Torchic, just breed a Treecko, put it on the GTS and ask for Torchic.
