Mewtwo Tag Perfection

This deck is set up to be the ideal Mewtwo & Mew (M&M) tag team deck. I only put three Mewtwo & Mew tag team cards in it since they give up 3 prize cards each you can only lose 2 before the game is over anyways, and if 1 is prized you're still good. 

Naganadel & Guzzlord tag (Nagalord) sits on the bench to allows you to discard pokemon you get in your hand to the discard pile so that M&M can use them and Giovanni's Exile gets them off the bench.

Ideally you'll top deck 1

This deck is set up to be the ideal Mewtwo & Mew (M&M) tag team deck. I only put three Mewtwo & Mew tag team cards in it since they give up 3 prize cards each you can only lose 2 before the game is over anyways, and if 1 is prized you're still good. 

Naganadel & Guzzlord tag (Nagalord) sits on the bench to allows you to discard pokemon you get in your hand to the discard pile so that M&M can use them and Giovanni's Exile gets them off the bench.

Ideally you'll top deck 1 M&M, 1 battle compressor, and a rainbow energy. With the battle compressor you would discard Mewtwo EX (XY-8) for attacks, Solgaleo for the GX attack and Tsareena to keep the opponent's active pokemon without energy and confused. 

For this deck you want to use a rainbow energy to use Solgaleo's GX attack ASAP so that you can attach 3 more rainbow / 2 psychic energy to your M&M in the early game. With all 4 rainbow energy he can copy any attack available in the deck immediately with just a Dimension Valley /  1 more Psychic energy including Mega Sableye & Tyranitar's (MST) Greedy Crush to get more prize cards against GX/EX opponents. If you exclude MST's Greedy Crush, then M&M can copy ANY OTHER ATTACK in the deck for only 2 total Rainbow energy and a Dimension Valley /  1 more Psychic energy.

Any early cherish balls / quick balls / Sonia's should be used to get Solgaleo in the discard pile to use Sol Burst in the early game. If you find Solgaleo is prized, or run into unusual trouble getting him out, then Nagalord's Chaotic Order is the intended backup to just take 2 prize cards to get a head start on the opponent.

Mewtwo GX (smp-196) has one of the highest damage GX/EX bench snipes in the game (tied only with Ho-Oh GX) that doesnt require discarding energy (Mega Latios EX, Hoopa EX & Raikou EX). Also with a Dimension Valley out, M&M can use Telekenisis for just 1 Psychic energy to deal 50 bench damage to 1 opponent. The Mewtwo EX (XY8) card is intended to provide the primary source of damaging attacks. Early on while building up energy you can use damage change to move any damage the opponent does back onto them and free heal yourself. Later in the game when you have more psychic energy attached you can start using Scatter Shot to do as much as 270 damage if you can get all the psychic energy attached to 1 M&M with Arceus & Dialga & Palkia GX tag team (ADP).

ADP & Mewtwo EX (XY12) allow you to attach energy to a pokemon straight from the deck or the discard pile. While Tapu Fini and Tsareena allow you to freely control which pokemon are in play on both sides of the board. 

Mega Scizor EX (XY9) provides utility and allows you to discard a special energy from the opponent or a stadium in play to keep them from gaining too much momentum and Mr. Mime protects the bench from snipe attacks. Since Solgaleo, Tsereena and Scizor cant be put onto the bench, you should consider choosing the 3 of them when you get a battle compressor.

Altaria GX (SM75) provides the deck's only decent shred attack and stops GXs from doing damage if you need to buy a round. Then Jolteon (G1) & Glaceon EX (XY10) stop both basic or evolution pokemon from doing damage. The strategy behind these 3 is that you use Tsareena in the early game to make them waste switch cards putting something back into play that isnt confused and has energy, so that in the end game you can use Altaria, Jolteon and Glaceon to stop them damaging you altogether, then using damage change when they actually do manage to damage you.  

If you dont want to use this strategy then I would recommend replacing Jolteon and Glaceon with Vileplume GX for a 1-2 energy 180 damage attack and then either Jirachi GX to get rid of Psychic type weakness or Naganadel GX for a better bench snipe damage.