Decklist from Jason Klaczynski.
This deck uses Medicham ex as its main attacker. Medicham ex is a Stage 1 with a disruptive Poké-Body, and two decent attacks. Its Poké-Body, Wise Aura, prevents Powers from non-ex Pokémon from being used. Its attacks are Pure Power, which costs two Colorless and lets you spread 3 damage counters however you like on the opponent's side, and Sky Kick, which does 60 damage for 3 Energy, and actually does more (a net 70) if the Defending Pokémon resists Fighting.
Lead with Jirachi or Meditite and aim to evolve into Medicham ex on turn 2. You play 4 Medicham ex, and 4 Professor Elm's Training Method to search for it. If you lead with Jirachi, you can use Swoop! Teleporter to swap it for Meditite.
Once Medicham ex is in play, start using Pure Power to pick away at their Bench. If you need to get more aggressive, attach a 3rd Energy and Sky Kick. Or, if you have Pow ready, attach Energy onto a second, Benched Medicham ex, let the Active Medicham ex die a natural death, then go nuts.
In the late-game, when your opponent is low on resources, you can Pow a vulnerable Pokémon Active, play Team Aqua Hideout to trap it there, then chip their Bench with Pure Power. This is similar to what Camler does, just that you have fewer copies of Team Aqua Hideout, and Pure Power does less damage overall than Split Bomb.
This deck uses the 4 Jirachi + 4 Swoop setup engine that was quite popular in 2005.
This deck has Island Cave, so you can use Jirachi's Wishing Star and wake it up with an Energy attachment. You can also attach Holon's Magneton to Medicham ex and return itself for a repeated Full Heal effect at the cost of your Energy attachment for the turn.
Wobbuffet hard counters ex's. Against some ex decks you can simply attach Energy onto it and Flip Over to victory, while against other ex decks it'll function as a wall to safely get Energy attachments on before you Swoop it away and evolve into Medicham ex.
Jirachi can be used as an attacker — that's what the Metal Energy is for! It hits Pokémon with Bodies for 50 damage, and can use both its Power and attack in the same turn if you have Island Cave and an Energy to wake it up after Wishing Star. It 2HKOs Safeguard Pokémon and Latios ex δ that wall Medicham ex. Against Rayquaza ex δ, you can Metallic Blow for 50, take 40 on the Special Circuit counterattack due to Metal Energy's -10, then Swoop to the 50 HP Meditite, evolve to Medicham ex, attach an Energy and Sky Kick for 60 and the KO.
This deck has the full 4 Pow and 4 Energy Removal 2 to screw with the opponent's Energy.
Different Meditites: The usual Meditites are the Psyshock and Fake Out ones, which can paralyze to disrupt opposing Jirachi early, or randomly clutch games late. The Psyshock one has 40 HP, so I prefer the Fake Out one. The other Meditite that can be considered is the one with Meditate, which can 1HKO a Pokémon that's at half its max HP with said attack.
Medicham ex comes with a built-in disruptive Poké-Body, which shuts down Jirachi and Pidgeot without the need to devote deck slots to Girafarig or Lunatone + Solrock, or the Holon Engine to find them.
Neither of Medicham ex's attacks are walled by Resistance.
Wise Aura doesn't shut down Powers from ex's, notably Electrode ex.
When your opponent doesn't have anything that's stopped by Wise Aura, Medicham ex plays like a bad Rayquaza ex δ. Both Pokémon are quite similar: 110 HP, ex, and an attack that does 30 to the Bench for 2 Energy. However, Medicham ex is a Stage 1, meaning you have to spend another card (Meditite) to bring it out, and can be targeted on its Psychic Weakness. Rayquaza ex δ has no Weakness, and has a useful cost reduction Poké-Body, as well as extra damage on Special Circuit under specific conditions.