Deoxys-EX is getting released in Japan in some time so here's an idea on what the card could do.
Deoxys-EX 170 HP sychic:
Ability: Mental
Once during your turn, you may search your deck for a sychic: energy card and attach it to this Pokémon. Shuffle your deck afterwards.
sychic:sychic::colorless: Psycho Boost 150
Discard all sychic: energy attached to Deoxys-EX.
Retreat: :colorless:
Weakness: sychic:
Resistance: ()
Mysterious Meteorite A - Trainer
Item
Pokemon Tool: Each Pokemon can have only 1 Pokemon Tool attached to it at any time.
If this card is attached to Deoxys-EX, put 5 damage counters on Deoxys-EX, and Deoxys-EX attacks do 50 more damage.
Mysterious Meteorite D - Trainer
Item
Pokemon Tool: Each Pokemon can have only 1 Pokemon Tool attached to it at any time.
If this card is attached to Deoxys-EX, resist damage done to Deoxys-EX by 100 and Deoxys-EX attacks do 50 less damage.
Mysterious Meteorite S - Trainer
Item
Pokemon Tool: Each Pokemon can have only 1 Pokemon Tool attached to it at any time.
If this card is attached to Deoxys-EX, your turn does not end when Deoxys-EX attacks.
ACE SPEC: You can’t have more than 1 ACE SPEC card in your deck.