Energy cards look simple next to a flashy Rare, but getting the balance wrong is one of the most common reasons a deck underperforms.
Basic Energy: the unlimited exception
Basic Energy cards are the one card type exempt from the standard 4-copy deck limit, because a deck needs a steady, dependable supply of Energy to actually attack. Most decks run somewhere between 8 and 12 Basic Energy depending on how Energy-hungry their attacks are.
Special Energy: powerful but limited
Special Energy cards add extra effects — bonus damage, healing, multi-type Energy — but count against the normal 4-copy limit like any other card. They're a build-around tool, not a replacement for your Basic Energy base.
The one-per-turn rule
You can only attach one Energy card per turn under normal rules, which is why Energy acceleration effects (cards or Abilities that attach extra Energy) are so valuable in faster decks.
Frequently asked questions
Why can you run unlimited Basic Energy but only 4 of everything else?
Decks need a reliable, plentiful source of Energy, so Basic Energy is exempt from the 4-copy limit.
What does Special Energy do that Basic Energy doesn't?
It adds extra effects but is limited to 4 copies per deck.
Can you attach more than one Energy per turn?
Normally just one, unless a card effect says otherwise.