I don't know why people stopped playing with mardu dragons decks. In my opinion, it's one of the best meta. Especially now, when mardu dragons are very strong even without Stormbreath Dragon. My version includes some candies like Monastery Mentor. With seven dragon creatures, two Sarkhan, the Dragonspeaker and Dragonmaster Outcast there is pretty high chance to have a dragon while casting dragon-friendly spells: Draconic Roar and Foul-Tongue Invocation what makes this deck even stronger.
Removals:
Crackling Doom - used in deck where it should be played - mardu deck, not some fancy, never-get-right-mana black-jeskai deck.
Draconic Roar - best direct damage spell in the format. Makes your opponent cry when used with Soulfire Grand Master
Foul-Tongue Invocation - another dragon-friendly removal. Repairs your life when you were pushed hard at early game.
Kolaghan's Command - it's a decent card. I put this because it can work great with Dragonmaster Outcast and can kill the One and Wonderfull One Man Army Jace, Vryn's Prodigy
one turn after he enteres the game. Not to mention other Origins planeswalkers.
Murderous Cut - with so many expensive cards, you need to reposnose with as low mana spells, as possible. Murderous Cut has a master degree in killing by suprise and by low cost.
Creatures:
Kolaghan, the Storm's Fury - bread and butter in this deck. Does everything you need - hits hard! Pretty sweet, when you have another dragon on the table already. No need to say more.
Dragonlord Kolaghan - he has not seen many plays in standard, but just like Monastery Mentor can do some serious work in this deck. 6/5 flying, haste and additional threat?! - come on!
Dragonmaster Outcast - i haven't played so many games with this deck to be sure if this card is fitting to the rest, but i belive that all the removal spells and Kolaghan's Command can protect him till the first dragon token. And as we know, dragons are good. Dragons good -> Dragonmaster Outcast good.
Thunderbreak Regent - another best creature :) Deals 3 dmg at least (counters doesn't matters, these are for weak wizards). 4/4 fly for 4 mana?!
Monastery Mentor - he's great due to a fact, that this deck plays 4 Planeswalkers, and 17 other non-creature, non-land cards. That means, that he can create your defense, until you will be able to cast any (other) serious threat. I don't know, why this card was never played in standard in T1 decks. Maybe because he is vulnerable to fast removal spells, and those were significantly reduced in last rotation. Now it's his time to shine.
Soulfire Grand Master - until Jace, Vryn's Prodigy, best two drop in the format. Optimal gives you 6 life in 3rd turn with Draconic Roar. Stops 1/x creatures from attacking. Buybacks spells. Two mana drop. Works great with more than a half instants and/or sorcery spells in this deck. Lack of this guy in the few first turns can hurt a lot, so the best starting hand is the one with two lands that can cast him and himself.
Planeswalkers:
Ob Nixilis Reignited - I gave him a chance instead of 3rd Sarkhan, the Dragonspeaker and he's a game changer. This card provides you with two of the most important things: table control and card gain.
Sarkhan, the Dragonspeaker - another card that goes very cheap and was underestimated, but he didn't deserve this. I love this guy! Very often after you cast him, he will make your opponent to rage quit or throw the cards, because if he doesn't have any response, he will be DEVASTED! Sarkhan enters like a boss. I mean, like this:
Sorin, Solemn Visitor - cheapest of all planeswalkers in the deck. Can defend himself and gives a nice boost of life with any dragon. Properly protected can turn into an emblem, which should be not a problem. More probably, you'll win the game earlier.
Others:
Duress - at early game this deck is pretty vulnerable to non-creature threats, like planeswalkers, counters, burn spells and so on. Duress has been always a good friend to mid range black decks. Try to alway play it, before casting Soulfire Grand Master or Monastery Mentor.
Haven of the Spirit Dragon - helps cast dragons, especially Thunderbreak Regent who has symbol:RR in cost. Doesn't have to say, that this brings your dead guys back.
Outpost Siege - I'm not sure about this - it doesn't have an immediate impact on the game, but sometimes it's worth - especially, when the game allows you to rest one turn. Still testing this card.
Sideboard:
Crackling Doom - if 3 is not enough. Best against deck with many, big creatures (i.e. eldrazi deck).
Crux of Fate - against decks with many annoying, non-token creatures. I would say, against mid-ragne decks this works the best, because probably you will have some dragons on your table. Slower than languish, but doesn't hurt your dragons.
Languish - if situation gets out of control, and you must wipe the board fast. The best thing is - the planeswalkers and kolaghan's stays.
Radiant Flames - against token decks. Gives you tons of life with Soulfire Grand Master (he dies right after the damage is dealt).
Ruinous Path - against decks with fast planeswalkers (two-three mana) and other planeswalkers. Sometimes it's worth to wait a turn to cast it with awaken.
Transgress the Mind - against deck with high cost cards (like this one) and when Duress is not enough (like creature decks).
Ultimate Price - can be repleced with Dragonlord Kolaghan when 2 dmg is too low or Crackling Doom when opponent has many same creatures.
Utter End - best removal for annoying enchantmens, artifacts and planeswalkers stuff. The best is, that it works with instant speed!