2021-06-18 If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs
Horror Energy was included in the Rebel Clash expansion for Pokemon Sword and Shield, released in English on May 1, 2020
As a 1/1 for one mana that's not too bad, although modern casual decks would want a bigger power from a one-drop to beat like 2/1 with a weakness for the same mana at common Jungle Lion or a 1/1 with a better ability like fellow common Llanowar Elves or Essence Warden
Ok Official Pokemon Trading Card Game Perfect Guide (Strategy Guide) Details All prices are the current market price
Ancestral Illusions doesn't even help with things like Ivory Tower triggers or provide a great pool of unknowns for your opponent as three actually dead cards in hand would do
However, with Base Set cards continuing to climb in price, more and more collectors are aiming their sights at sets like Fossil