Hellkite Charger
Creature — Dragon
Flying, haste
Whenever this creature attacks, you may pay 
. If you do, untap all attacking creatures and after this phase, there is an additional combat phase.
Jaime Jones
Commander 2017 (C17)
• #138Rulings
You decide whether to pay {5}{R}{R} as Hellkite Charger’s ability resolves.
(wotc • 2009-10-01)
Hellkite Charger’s ability may trigger multiple times in the same turn, since its own ability gives it multiple chances to attack. Each time it resolves, you may create an additional combat phase.
(wotc • 2009-10-01)
If you pay {5}{R}{R}, the new combat phase immediately follows the current combat phase. There is no main phase in between.
(wotc • 2009-10-01)
If two Hellkite Chargers attack at the same time, both of their abilities trigger. If you pay {5}{R}{R} for each, two new combat phases will be created. However, all attacking creatures untap as those abilities resolve, not as the combat phases start. Any creature that attacks in the second combat phase will remain tapped during the third combat phase.
(wotc • 2009-10-01)
Rulings
You decide whether to pay {5}{R}{R} as Hellkite Charger’s ability resolves.
(wotc • 2009-10-01)
Hellkite Charger’s ability may trigger multiple times in the same turn, since its own ability gives it multiple chances to attack. Each time it resolves, you may create an additional combat phase.
(wotc • 2009-10-01)
If you pay {5}{R}{R}, the new combat phase immediately follows the current combat phase. There is no main phase in between.
(wotc • 2009-10-01)
If two Hellkite Chargers attack at the same time, both of their abilities trigger. If you pay {5}{R}{R} for each, two new combat phases will be created. However, all attacking creatures untap as those abilities resolve, not as the combat phases start. Any creature that attacks in the second combat phase will remain tapped during the third combat phase.
(wotc • 2009-10-01)