Been a busy few weeks! More decks to come, but for now, let's start off with one I've been tinkering around with.
In a Mirror Darkly (Double Yveltal BA-Deck)
Pokémon: 16
4 Yveltal (XY 78)
4 Zorua
4 Zoroark
2 Scraggy
2 Scrafty
Trainers: 30
4 Professor Sycamore
4 Shauna
2 Trevor
2 Pokémon Fan Club
2 Lysandre
2 Energy Retrieval
2 Professor's Letter
2 Switch
4 Ultra Ball
4 Muscle Band
2 Magnetic Storm
Energy: 14
12 Darkness Energy (Foil)
2 Darkness Energy
Strategy: While hurt by the absence of Yveltal-EX, Shadow Circle and Double Colorless Energy, (XY) Yveltal is still capable of helping to power up other Yveltal and Zoroark in a hurry. Zoroark... well, I'll be honest. I wish it was the Legendary Treasures version. I'd even take the Black/White Foul Play version as a reprint. As it stands, one Darkness for 30 and preventing retreat won't win you battles, and Night Claw really wishes it had Double Colorless Energy to go with a Darkness Energy attached by Yveltal. At least Trick Coin reduces your odds of having to discard Energy.
For a bit more oomph, consider more Scrafty and less Zoroark. Machine Gun Headbutt takes only one Energy attachment on top of an Oblivion Wing, but comes with its share of flips. Without Trick Coin, on average, you get 75 damage out of two Darkness Energy. With Trick Coin... things get complicated. Working on the assumption you reflip if you get less than two heads, your average damage comes out to around...
* 93.5 (12.5% x 150, 37.5% x 100, and the remaining 50% being broken down into a 1:3:3:1 ratio of 0/50/100/150 damage) if you're willing to take a higher risk of doing 0 damage, or...
* 84.375 damage with a 1/16 chance of doing 0 damage (reflip only on three tails, where doing 0 damage again would take 6 tails in a row).
You still want to retreat out of this, to get out of Confusion damage counters, and a Darkrai-EX (even just one in the deck) can take you real far with accomplishing this, if you can get your hands on one.
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Added on 12/28/14:
Floating Fairies (Double Xerneas BA-Deck)
Pokémon: 13
4 Xerneas
4 Carbink
3 Spritzee
2 Aromatisse
Trainers: 32
4 Professor Sycamore
4 Tierno
2 Trevor
2 Pokémon Fan Club
2 Pokémon Center Lady
2 Lysandre
2 Energy Retrieval
2 Evosoda
2 Professor's Letter
4 Ultra Ball
4 Hard Charm
2 Fairy Garden
Energy: 15
12 Fairy Energy (Foil)
3 Fairy Energy
Strategy: This functions as most decks with Xerneas and Aromatisse do. Xerneas's first attack accelerates the flow of basic Fairy Energy into play, while Aromatisse's Ability directs said Energy to the Pokémon that need it the most. Carbink functions as a secondary attacker, though it has significantly lower amounts of HP than Xerneas does. Sylveon can be considered for that position of secondary attacker if you feel the disruption of its first attack and extra 20 HP outweigh the lower damage potential of its second attack and need for Evolution to enter play, in comparison to those traits of Carbink.
Were EXP Share (back) in the format, I would suggest it as an additional Pokémon Tool to consider adding to this deck. Until the Japanese set in which it is reprinted comes out, this is advice that will have to be waited on. Though there are certain ways to restore Energy from the discard pile in this deck (Energy Retrieval), they do not keep the Energy attached to Pokémon in play. The best you can manage with these cards is to use Hard Charm and Pokémon Center Lady to keep your higher HP Pokémon around and in the battle. [EDIT, February 1, 2015: once Primal Clash is tournament-legal, if you play by these rules, this will become a valid option and suggestion.]
The Trainers provided are definitely solid. Four Professor Sycamore and Tierno can help you power through the deck, and most of the other things available are usable as soon as they enter your hand, allowing you to prepare for the next Professor Sycamore. The Pokémon Fan Club help with the lowered Basic Pokémon count, but you may feel like you need to acquire and add more. More Evosoda can be added if you feel that you need it to get Aromatisse into play sooner, but will be dead weight once there are no more Evolution cards left in the deck. More Fairy Garden are available for you to work with, helping you win Stadium wars with your opponent if you choose to add them as well as helping to maintain a zero Retreat Cost for your Pokémon.
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Destructive Interference (Battle Arena Hybrid)
Pokémon: 18
2 Xerneas
2 Xerneas (Promo)
2 Spritzee
1 Aromatisse
3 Jigglypuff
2 Wigglytuff
2 Carbink
2 Yveltal
2 Yveltal (Promo)
Trainers: 28
4 Professor Sycamore
2 Pokémon Fan Club
2 Shauna
2 Tierno
2 Lysandre
2 Energy Retrieval
2 Evosoda
2 Professor's Letter
4 Ultra Ball
2 Hard Charm
2 Muscle Band
2 Fairy Garden
Energy: 14
6 Fairy Energy (Foil)
3 Fairy Energy
5 Darkness Energy (Foil)
Strategy: Oof. Without the traditional double-deck, the thin Evolution lines hurt this set-up. What it lacks in Pokémon that work together well, it makes up for with an array of useful Trainers. While I hate to say "take the Trainers from this and add them to more useful Pokémon", that's really the best advice I'd offer. If, however, you are restricted to the Pokémon from this deck, I would say that the Pokémon that most benefit from the Legendary presences are Aromatisse (for its Ability), Wigglytuff (for added Energy acceleration), and Carbink as an additional attacker. The focus shifts primarily to Fairy-types, and could even run the 2-2 Sylveon line without Yveltal (with a replacement of Darkness Energy with Fairy Energy).