From Bulbapedia, the community-driven Pokémon encyclopedia.
Mega Audino EX was a Pokémon Trading Card Game deck archetype played in the very end of the 2015-2016 season with great results. The deck's strategy revolved around M Audino-EX being able to damage benched Pokémon and get easy knockouts against Night March decks. This deck was notable for many players not expecting M Audino-EX to be successful due to its low setup and damage compared to Mega Rayquaza EX, another Mega Pokémon, and other Pokémon-EX decks. Mega Audino EX deck unexpectedly ranked first place in the 2016 Pokémon Trading Card Game World Championships Master Division, and Champion Shintaro Ito's version was printed as a promotional World Championships deck, Magical Symphony.
Strategy
The deck aimed to use M Audino-EX as the main attacker. Its Magical Symphony Attack dealt 110 damage to the Active Pokémon plus 50 to a Benched Pokémon when a Supporter card was played that turn, so many Supporter cards were optimal in the decklist. The bench damage could notably knock out opposing Joltik, Combee and Eevee in a single attack. Metal energies were used in the list to benefit from Magearna-EX's Mystic Heart Ability, preventing effects of attacks other than damage to M Audino-EX, and use Cobalion as a secondary attacker. Absol was also played to move 3 damage counters between opposing Pokémon and often score extra knockouts. Audino Spirit Link and Mega Turbo are other notable supporting cards.
Typical decklist
Shintaro Ito's decklist at the 2016 World Championship
Reasons for the loss of playability
Mega Audino was a successful deck due to the favorable matchup against Night March. As Night March was rotated out of the Standard format right after Worlds, M Audino-EX struggled to deal against decks with less frail Pokémon. In the Expanded format, other Pokémon were better at dealing against Night March and Mr. Mime was a common card in Expanded decks to prevent benched damage.