And as you see and has been commented also, it goes with 10 energies.
The core of any deck are the trainers. Will make you get the desired card, in the right moment. that's why you build with +30 of them. The other, goes to pokémon and energies. And if you need something to play, add more than 1.
With the Garchomp deck example, 1 high HP hard hitter (Garchomp) and its evo line 4-1-4 to 4-3-4 with rare candies. Jumping over the middle stage wins you time as you don't plan to attack with that but to get the final stage ASAP. Unless something very special, like could be Servine FCO6 to use an ability.
Then add some partners, in this case, Lucario with Riolu. A consistent line to help the hitter (2-2, 2-3, 2-1...) and possible extra techs like Oranguru or like could be Tapu Lele GX and other.
The supporter staples for standard comprise more or less, always:
4 UB (or any other solution in Ball form to search pokémon)
2 Brigette if the deck demands her (Tapu Lele GX combo for 1st turn set up)
1-2 Acerola if fits the deck
Lillie (being more played recently)
Then the other trainers: Items (including tools) and stadiums. The most used items right now are
1-3 Float stone
1-3 Choice band
4 Puzzle of time
1-2 Field blower
Rescue stretcher or Super rod are also widely used. Evosoda became important as a lot of GX are Stage 1. And Fighting fury belt for basics, Also Nest ball or whatever fits in the deck (Rare candy, Switch, Prof letter, Energy loto, Energy switch, Multi switch...)
The previous deck is a bit special. Garchomp needs Cynthia to hit for 200. And Lucario looks for any card in deck. That's why no Sycamore, and you play Pal pad (to recover the Cynthias). That's why no Sycamore and no Guzma for example, your supporter have to be Cynthia, all turns.
And finally, the lower amount of energy to make it work. And 10 is good.
So in your deck you could play with Garchomp as hitter. Or with Buzzwole. Or with Zygarde. Or with a mix, even though, if Garchomp, you need more space for the evo line+candies as it's a stage 2. And you should want to focus on Garchomp's. And if you prefer Buzzwole, or Buzz/Zygarde, then remove all Garchomp to have a lot of space and get 3 Buzz and 2 Zygarde, or 4 of one. And a couple of Regirock to help hit harder.
Pidgeot could be a good spare tech, although the Mega is not as good as attacker and you need also the Link to don't loose a turn. Again, out of your main strategy, you could add one, as tech. But if it's going to be important, then add 2, 3 or 4, for consistency. You don't want something you need is prized. On the other side, adding so much Pidgeot, then you should focus your strategy on a different deck and it's actually not so good. It never seen high level play not even when released (so I would remove it to make space).
As for trainers, add some more staples. It depends on if you want to make a Garchomp deck, or just another mix or different deck but, choose a core close to the staple.
Finally cut the energies to 13 to start, and try, what you miss, what you don't use, make changes, remove energies, add techs, change items... That's how a good deck is made
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