Astrid

Astrid is a Pokémon Trainer who has the ability of Mega Evolution, and has an Absolite and Key stone in her possession.

Mega Evolution Special
Astrid met Alain in a forest and Alain challenged her for a battle. Alain sent out his Charizard and Astrid noticed the Mega Stone it was wearing. Astrid then asked Alain's name and introduced herself after Alain had done his. She sent out her Absol who wore a Mega Stone aswell. After Absol blocked a few attacks from Charizard, Alain said that Absol was trained well. Both Alain and Astrid then Mega Evolved their Pokémon.

Absol was able to stop and defend itself from several attacks of Charizard. Astrid then ordered her Absol to use Dark Pulse but Charizard used Blast Burn which overwhelmed Absol and was able to knock Absol out. Astrid went to her Absol, who reverted back to its normal form, and said that it fought well. She was then approached by Alain who wished to fight her again in the future which Astrid agreed to.

Diancie and the Cocoon of Destruction
Astrid appeared at the beginning of the movie where she fought against Ash Ketchum. She used her Pyroar against Ash's Pikachu which Pyroar was defeated by Pikachu's Electro Ball. Her Meowstic then faced against Ash's Froakie, who was knocked out by Meowstic's Charge Beam. Astrid then sent out her Absol and also Mega Evolved it to battle against Ash's Hawlucha. Hawlucha tried to defeat Absol by using several of its attack but was later knocked out by Absol's Dark Pulse. Ash thanked her for the great battle and Bonnie went to her and asked Astrid to marry Clemont. This surprised Astrid but Clemont dragged quickly Bonnie away.

Trivia

 * Astrid's design is of the generic female Ace Trainer from Pokémon X and Y.
 * She wears her Key stone as an earring.