Miraidon ex

Intro

Miraidon ex is a deck that has seen better days. The rotation of F Regulation Mark cards took out several setup pieces like Rotom V, Lumineon V, and Forest Seal Stone, as well as a big damage attacker in Raichu V (for which there is still no good replacement in SV Block). After rotation, Joltik Box took up Miraidon ex's mantle, using the same Miraidon ex + Iron Hands ex + Lightning-type Energy accelerator core, paired with attackers that could actually one-shot opposing Pokémon. Four Masters played Miraidon ex at Worlds; none of them made Day 2, but they fared better than the Ethan's Typhlosion players.

The deck put up better finishes post-BLK/WHT, getting 9th at Special Event Buenos Aires and going 10-3-1 at Regionals Toronto and Seattle, with lists that were only 1 card (a 70 HP Magnemite) off from being legal in SV Block. It should be noted, though, that this newfound level of success was also due to other decks changing in a way that made them softer to Miraidon ex: Gholdengo ex incorporated the Lunatone + Solrock engine, which presented more targets to Amp for 2 Prizes with Iron Hands ex.

Game Plan

Get Miraidon ex into play and use Tandem Unit to search for Iron Hands ex and Magnemite/Tynamo. Use all resources at your disposal to charge up Iron Hands ex or Miraidon ex: Electric Generator, Magneton/Eelektrik, even Magnemite or Squawkabilly ex's attacks are options. Squawk and Seize, Professor's Research, and Carmine let you speed through your deck, drawing into more copies of Electric Generator while discarding excess Lightning Energy for Magneton/Eelektrik.

Once you have an attacker charged, use Boss's Orders or Prime Catcher if necessary to choose your targets. Gust out evolving Basics/Stage 1s and KO them with Iron Hands ex's Amp You Very Much to be as disruptive as possible. If your opponent puts down a Basic ex liability (like Fezandipiti ex after you've Amped their evolving Basic), go after it with Miraidon ex before they Turo it back to hand. Your damage output is not as high as Joltik Box's, but your Energy acceleration is much stronger, so seize opportunities to score KOs before they slip away (e.g. opponent Turo-ing liabilities, or evolving out of Amp range).

Attackers

Iron Hands ex is your first attacker. It's meant to go after evolving Basics/Stage 1s, which almost every deck plays, taking 2 Prizes for the KO with Amp You Very Much and denying the evolution.

Miraidon ex is your next attacker. It can KO Basic ex Bench-sitters like Fezandipiti ex, Latias ex, Ogerpon ex (other than Cornerstone Mask), and Genesect ex. If you have Defiance Band, it can KO Raging Bolt ex and Terapagos ex too.

Zekrom ex is your mid/late-game attacker. If your opponent has taken 3 Prizes (usually after losing your first attacker and blowing up Magneton), it hits 280 damage, enough to KO Basic and Stage 1 ex's. If your opponent has taken 4 Prizes, it hits 330 damage, enough to KO Stage 2 ex's.

Bloodmoon Ursaluna ex is your other late-game attacker. Its damage output is slightly higher than Miraidon ex's, and requires less Energy to attack if your opponent is down to 1/2 Prizes.

First or Second?

Carmine builds want to go first. Going first also lets you score KOs on your opponent's Basics with Iron Hands ex before they can evolve.

Arven builds want to go second. Going second lets you Arven for Electric Generator on T1, as well as use Magnemite's or Squawkabilly ex's attacks to accelerate Energy.

ACE SPEC

Prime Catcher. This deck is fast, and needs to be able to force out high-HP Pokémon for softer targets on the Bench. 

Variants

The first big decision you'll have to make is whether you want to play Magneton or Eelektrik (or even both) as your Energy accelerator. Pros and cons of each:

• Magnemite has more HP than Tynamo, and the PAL Magnemite has a setup attack. Magneton KOs itself when it uses it Ability, but this can be beneficial in turning on comeback cards (Zekrom ex, Defiance Band, Counter Gain), and clearing space on your Bench. Magneton is also harder to trap than Eelektrik, since it can blow itself up and has 1 Retreat Cost.

• Tynamo has 0 Retreat Cost. Eelektrik accelerates Energy slowly, but can be used more than once. Eelektrik can accelerate to non-Lightning Pokémon like Mew ex.

Your choice of Energy accelerator also influences your secondary setup Supporter. Magneton prefers Carmine, as the extra discard helps you reach 3 Lightning Energy in the discard pile for a full Overvolt Discharge. Eelektrik prefers Arven and at least 1 Air Balloon to help Eelektrik escape if it's Bossed.

Other Options

• Ethan's Pichu: Good attacker into Budew (which shuts off Electric Generator), KOing it for 0 Energy while giving you 2 new cards (the Prize for the KO + 1 from its draw effect).

• Zeraora: ex Bench sniper. Instead of Bossing for game, you can load up a Zeraora and snipe the opponent's Benched Fezandipiti ex or Latias ex. Note that you can't go after Ogerpon ex's, as they are Teras and have Bench damage protection.

• Tapu Koko ex (Vengeful Shock): Pseudo-damage mod. After a KO, you can Vengeful Shock for 120 and Paralysis. If your opponent doesn't have a switch/Scoop Up card and misses their attack, you can clean up with any attacker. This can lead to a 3-Prize KO if their Pokémon is an ex with 240 HP or less and you finish them off with Amp You Very Much.

• Pokémon Catcher: Replaces Boss's Orders. Pokémon Catcher can be used if you've used or are using another Supporter that turn. However, to make up for its unreliability, you need to add 2 Catchers for every Boss removed, which means fewer deck slots available for other cards.

• Bravery Charm, Defiance Band, Counter Gain, Future Booster Energy Capsule: Utility Tools.

• Academy at Night: Can stash a card before you Research/Carmine, set up Electric Generator if it's a Lightning Energy, or bump an opposing Stadium.

Tips

• Always thin your deck with Nest/Ultra Ball searches before playing Electric Generator.

• Electric Generator and Dynamotor only work on Benched Pokémon, so having a free retreater like Mew ex, Latias ex, or even Tynamo is useful for sticking in the Active Spot after a KO. Use your Energy acceleration effects to charge up a Benched attacker, then retreat for free into it and return the KO.

• Unlike Electrode ex from RS-PK, Magneton cannot attach Energy that was on itself when it blows itself up. If you have 1 Energy on Magneton and need to discard it so that it can be attached to something else, use Switch/Prime Catcher to send it to the Active Spot (or promote it after a KO), then retreat it to your attacker. This works even if you have Latias ex out, as Magneton is not a Basic Pokémon and doesn't get the Retreat reduction.

• Super Rod can be used to increase the amount of Lightning Energy in your deck for Electric Generator. However, Magneton/Eelektrik want Energy in the discard pile. Try to shuffle Energy back only if you can't blow Magneton, or if you would still have 2-3 Energy in the discard after using Super Rod.