The central theme of the deck is, obviously, Dragons. Cast them, protect them, love them. The protection works even better by using 2 cards. Monastery Siege will force your opponent to pay at least 2 more mana to target one of your Dragons. While this might seem a small price to pay, consider the following scenario: You are low on HP and two Icefall Regents attack you, while your opponent has cast Monastery Siege for Dragons. This means that targeting both Dragons with a removal spell needs +8 mana. Which means that casting, for example, 2 Doom Blades would actually cost you 12 mana. Your opponent will find killing your Dragons even less appealing if he is damaged by the process. That's when you introduce him to Thunderbreak Regent. But, even if your opponent is a psycho and really wants to kill your creatures to reenact the events that lead to the Khans of Tarkir timeline, Dragon Tempest makes sure that your Dragons will attack at least once before dying, and that they will do some extra damage in the process.
Moving on, we can see a really underestimated card: Foe-Razer Regent. While he DOES seem hard to cast and his effect IS a bit mediocre, he becomes a tremendous force with a helping hand from Frontier Siege. Most creatures are weaker than Dragons. So, what if your Thunderbreak Regent enters the battlefield as a 6/6, or your Dragonlord Dromoka as a 7/9, all while killing an opponent's creature in the process?
Dromoka and Surrak do not need much introductions. They make your creatures uncounterable.
But the real star of the deck is Sarkhan. In several games, while using my five-colored Modern Dragon deck, he actually saved me. He worked as a mana fixer when I lacked a certain color. He helped me add more mana when facing decks like the ones that destroy lands. He let me draw cards, thus helping me cast my spells faster. And he protected me, when needed, by having a 4/4 Dragon enter the battlefield. And his ultimate ability is just perfect.
Ideal opening hand:
2x Mountain, 1x Forest, 1x Atarka's Command, 1x Dragonlord's Servant, 1x Thunderbreak Regent, 1x Rattleclaw Mystic
Turn 1: Mountain, Pass
Turn 2: If you draw land: Forest, Atarka's Command, extra land and 3 damage, pass.
If you don't draw land: Mountain, Dragonlord's Servant, pass.
Turn 3: Land, Thunderbreak Regent. And the rest is history.
Alternative way to move:
Turn 1: Forest, Elvish Mystic
Turn 2: Island, Verdant Haven
Turn 3: Mountain, Savage Knuckleblade with haste, enter combat.
So far, the deck has faced successfully aggro, mid-range and late game decks, winning at least 8/10 games each time (losing only due to mana flood sometimes).
Any feedback is welcome!