How does Abilities works?

[SoniMail]

Hello!
I've been collecting Pokemon TCG in the past months.
At first I only wanna collect the cards, but now I wondering to battle.

This week I bought a lot of cards and it comes with 3 decks the seller used to use. One of those decks really get my attention.
It has a Mewtow EX, which is a great card, and a Gardevoir, who have the ability to make each psychic energy count as 2. Used together, they seem to be a powerful combination.

My doubt is: how does Ability work? Gardevoir have to be my active Pokemon to use that? Or I can use that ability even if Gardevoir is in bench? If so, I've to activate that ability every round?

I know that's a noob question, but I didn't found the answer anywhere else.

Thanks guys!


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EDIT
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Other doubt: In Premier events I can only use cards released in the year of the event? A person I know just told me that in official events I can't use "old cards". Like, if I join an official event today, I wouldn't be allowed to use Next Destinies cards. is that true?

Thanks again

 

[PokePop]

Unless the Ability text states otherwise, the Pokemon just needs to be in Play. It doesn't need to be Active to use the Ability.
Some Abilities have to be activated. Some are always on. Go by the text. If it says "once per turn" or "as often as you like", then those need to be activated. If it doesn't say that, then it is always on. Gardevoir's Ability that doubles P energy is always on.

On the front page of Pokegym.net, in the upper left, you will find links to "Standard Legal Card List" and "Expanded Legal Card List".
Those will list all legal sets, AND cards from older sets that have been reprinted in legal sets, that can be used in those two formats.
Most Premiere events use Standard, but starting this year some Premiere events use Expanded.
All cards from Next Destinies are legal in Expanded and a number of them are also legal in Standard.
Sets remain legal in Standard for more than a year. Usually two to three years.