Pidgeotto's "Twister" attack says to discard an Energy attached to the Defending Pokemon for each heads flipped. Does that mean if I only flip one heads I cannot discard a Double Colorless Energy?

Actually, you can discard a DCE with a single heads. It's like paying a Retreat Cost with an Energy Card that has more energy than required to retreat. Total the number of flips, then discard Energy Cards one at a time until the condition has been met. So if you flip one heads you can discard a single Energy Card with one or more energy on it. But if you flip two heads you can either choose a card with one energy then another card with one or more energy, or you can choose a single card with two or more energy on it.

Relevant cards