Whirler Virtuoso

Some triggered abilities that state that you "may pay" a certain amount of energy describe an effect that happens "If you do." In that case, no player may take actions to try to stop the ability's effect after you make your choice. If the payment is followed by the phrase "When you do," then you'll choose any targets for that reflexive triggered ability and put it on the stack before players can take actions.

Energy counters are a kind of counter that a player may have. They're not associated with any specific permanents.

energy is the energy symbol. It represents one energy counter.