Blitzläuferin

Doppelschlag, Eile
Immer wenn die Blitzläuferin angreift, erhältst du {E}{E} (zwei Energiemarken), dann kannst du acht {E} bezahlen. Falls du bezahlst, enttappe alle Kreaturen, die du kontrollierst, und es gibt nach dieser Phase eine zusätzliche Kampfphase.

Coureuse d'éclairs

Double initiative, célérité
À chaque fois que la Coureuse d'éclairs attaque, vous gagnez {E}{E} (deux marqueurs « énergie »), puis vous pouvez payer huit {E}. Si vous payez, dégagez toutes les créatures que vous contrôlez et cette phase est suivie d'une phase de combat supplémentaire.

稲妻駆け

二段攻撃、速攻
稲妻駆けが攻撃するたび、{E}{E}（エネルギー・カウンター２個）を得る。その後、{E}８個を支払ってもよい。そうしたなら、あなたがコントロールしているすべてのクリーチャーをアンタップし、このフェイズの後に追加の戦闘フェイズを加える。

Lightning Runner

Double strike, haste
Whenever Lightning Runner attacks, you get {E}{E} (two energy counters), then you may pay eight {E}. If you pay, untap all creatures you control, and after this phase, there is an additional combat phase.

Modern Horizons 3 Commander

Aether Revolt

Double strike, haste
Whenever Lightning Runner attacks, you get {E}{E} (two energy counters), then you may pay {E}{E}{E}{E}{E}{E}{E}{E}. If you pay, untap all creatures you control, and after this phase, there is an additional combat phase.

Aether Revolt Promos

You untap all creatures you control, including ones that aren't attacking.

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

Energy counters aren't mana. They don't go away as steps, phases, and turns end, and effects that add mana "of any type" can't give you energy counters.

If a spell or ability with one or more targets states that you "may pay" some amount of {E}, and each permanent that it targets has become an illegal target, the spell or ability won't resolve. You can't pay any {E} even if you want to.

If an effect says you get one or more {E}, you get that many energy counters. To pay one or more {E}, you lose that many energy counters. You can't pay more energy counters than you have. Any effects that interact with counters a player gets, has, or loses can interact with energy counters.

Keep track of how many energy counters each player has. Potential ways to track this include writing theme down on paper or using dice, but any method that is clear and mutually agreeable is fine. (At higher levels of tournament play, dice may not be allowed for tracking counters that players have.)

Some spells and abilities that give you {E} may require targets. If each target chosen is an illegal target as that spell or ability tries to resolve, it won't resolve. You won't get any {E}.

Some triggered abilities state that you "may pay" a certain amount of {E}. You can't pay that amount multiple times to multiply the effect. You simply choose whether or not to pay that amount of {E} as the ability resolves.

Some triggered abilities that state that you "may pay" a certain amount of {E} 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.

{E} is the energy symbol. It represents one energy counter.