For the Baton pass team, there is one simple way to anihilate her: Taunt. My Mega Gardevoir demolished her, KOing 4 out of 6 Pokémon whitout taking a signle damage. I used the regular set:
Gardevoir @ Gardevoirite
EVs: 16 HP / 8 Def / 232 SpA / 252 Spe
Pre-Mega ability in Trace is also very usefull against weather sweepers, copying Sand Ruch and Ice Cleats to counter sweep. She also outspeed few dangerous Pokemon against the Champion: Kyurem, Flygon on the turn it mega evolves (if you play in Hard mode, otherwise she may outspeed in easy) and D.Haxorus if you don’t Focus Blast (or Focus Miss as I call it).
London’s Mega reunicluss looks hard to deal whit, so a priority user to counter his Trick Room is nice. I used Swords Dance Scizor, but any non-fighting type strong priority would do the job, like D. Haxorus Aqua Jet/Bullet Punch. As long as you deal whit Delta Reuniclus and the Trick Room run out, you are 100% safe. Just don’t let his Jellisent set it back
Excadrill is also amaising against E4.
I suggest something like this:
Mega Gardevoir (or any good offensive taunt user)
Any other Pokemon of your choice, look out for your team overall type synergy.
Just in case, my own team was:
Adamant Armorded Tyranitar: Stealth rock, Stone Eadge, Crunch, Superpower.
Adamant Sand Rush Excadrill: Iron Head, Earthquake, Rapid Spin, X-Scisor.
Timid Rotom-H: Overheat, Thunderbolt, Toxic, Thunder wave.
Adamant Scizor: Swords Dance, Bullet Punch, Superpower, Bug Bite.
Choice Scarf Modest D. Charizard: Shadow Ball, Dragon Pulse, Sludge Bomb, Dark Matter (didn’t have somthing for the fourth mooveslot).
Result? I DEMOLISHED the E4 in normal mode. Excadrill sweeps 3 out of 5 battle and Scizor anihilated London. Excadrill was very usefull against the sandstorm and tyranitar was amasing to counter the hail and Gardevoir tear appart Baton Pass.
If you want to copy my team, you could switch D. Zard for Giratina if you wish.