I will order them by mana cost and explain why they are in the deck.
1.-
Thunderbreak Regent
: This is by far the best dragon with a CMC of 4. A 4/4 red flyer for 4 mana? Sure. Being this a tribal deck, it makes his ability a lot more valuable, because if you get your opponents low enough, this dragon will disencourage them to throw their removal. With the help of our ramp package, you usually cast it at turn 3. In conclusion, it is a really good early beater with a very impactful ability.
2.-
Glorybringer
: This is the newest addition to the deck. It has haste, and you should almost everytime exert him, because its a free removal spell, and this deck needs them to be able to swing without the fear of dying. One of the all-stars of the deck for sure, but I would recommend waiting for it to rotate out of standard before purchasing it.
3.-
Thundermaw Hellkite
: One of the best dragons in this deck. Just his stats (5/5, flying, haste) make him a pain in the ass for the oponent but the main reason why it is in this deck is for the combos. The last ability is a game changer. It destroys any chumpblockers the opponents may have, giving you the opportunity to deliver the final blow.
4.-
Atarka, World Render
: This is the most synergistic dragon of the deck. If your opponents do not kill her before she can turn sideways and don't have flyers, they lose the game 100% of the time. By the time you cast her, you should have at least another dragon on board, so her ability of giving double strike is going to be so important to close out the game. Furthermore, she has trample, so good luck for your opponent trying to chumpblock her. The true star of the deck and a really good removal dark hole.
5.-
Dragonlord Atarka
: There's not much to say about the card that isn't self-explanatory. 8/8 trampler that deals 5 damage distributed as you choose is just good. Never feel bad tapping out to cast her, as she can win the game by herself.