Thundermaw Hellkite
Creature — Dragon
Flying
Haste (This creature can attack and 
as soon as it comes under your control.)
When this creature enters, it deals 1 damage to each creature with flying your opponents control. Tap those creatures.
Svetlin Velinov
Iconic Masters (IMA)
• #149Rulings
Thundermaw Hellkite will deal 1 damage to each creature with flying your opponents control whether those creatures are tapped or untapped.
(wotc • 2017-11-17)
If the damage that would be dealt to a creature with flying is prevented, that creature will still be tapped. If that damage is redirected to another creature, the creature with flying will be tapped, not necessarily the creature that ultimately was dealt damage.
(wotc • 2017-11-17)
Rulings
Thundermaw Hellkite will deal 1 damage to each creature with flying your opponents control whether those creatures are tapped or untapped.
(wotc • 2017-11-17)
If the damage that would be dealt to a creature with flying is prevented, that creature will still be tapped. If that damage is redirected to another creature, the creature with flying will be tapped, not necessarily the creature that ultimately was dealt damage.
(wotc • 2017-11-17)