Cheapest priced copy (Starter Commander Decks): $1.29 at Card Kingdom, near mint, their price list as of .
Thundermaw Hellkite 
Creature — Dragon · 5/5 · Mythic · Iconic Masters · #149
Flying
Haste (This creature can attack and {T} 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.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
3 printings · $1.29 to $17.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Iconic Masters | 149 | Mythic | $2.79 | $11.99 |
| Magic 2013 | 150 | Mythic | $2.29 | $17.99 |
| Starter Commander Decks | 164 | Mythic | $1.29 | — |
2 rulings from Wizards of the Coast
- 17 November 2017Thundermaw Hellkite will deal 1 damage to each creature with flying your opponents control whether those creatures are tapped or untapped.
- 17 November 2017If 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.