We now know all five of the dragonlords, which are the mythic powered up versions of the rather lackluster Fate Reforged cycle. All of the dragonlords certainly have the Baneslayer Angel quality of being these huge threats that might die to removal, but they also inversely force you to have that removal. Of the five Dragonlord Ojutai is my favorite, and the one I expect to have the greatest impact. Again, it's simply cheaper than the others - see Atarka's Command and Thassa, God of the Sea. This doesn't sell it on its own, but it helps. Unlike the other dragonlords, Dragonlord Ojutai has some built in protection with hexproof keeping it safe from your opponent's targeted removal. You'll need to give up that protection in order to swing, though notice that it's only when it's untapped not simply while attacking. If you find a way to give Dragonlord Ojutai vigilance or something to untap it in response to removal it gets hexproof again. Not only do you get to smack your opponent for five damage when you connect - a nice four turn clock, but you get to start Anticipate-ing for free. So even if your opponent manages to deal with Dragonlord Ojutai later you've gotten to replace it with one or two of the best cards from the top of your deck. Dragonlord Ojutai may end up playing a similar role that we've seen Prognostic Sphinx, though I suspect we might have to wait to see Dragonlord Ojutai mature into the next format change. Its casting post, power, and toughness don't stack up super well against Elspeth, Sun's Champion, Stoke the Flames, or blocking Siege Rhino profitably. Also keep an eye on Dragonlord Atarka, she's expensive but she has an immediate board impact, potentially sweeping up a creature and/or planeswalker or two and then leaving behind a flying trample 8/8.
I'm not 100% sure what kind of deck wants it, but Mirror Mockery is the kind of card that's just sending out all the right signals. It has way too many good interactions for it to sit around in the junk bin. Here are just a few to think about. You could slap it on your opponent's Siege Rhino and make it a decently effective removal spell. They can't really attack you any more with that creature. Even if it's a creature that does trade with itself, you're still buying yourself a removal spell and a bunch of time since they can't really attack with any of their smaller creatures either. If you're not at a low life total, you can just start eating their team until you finally need to trade off for the big one. Granted it's a little more risky to suit your own stuff, but how about suiting up your own Snapcaster Mage for free flashbacks? It works pretty well with any enter the battlefield abilities, like say the titans. Sun Titan can even recur the Mirror Mockery itself. Mirror Mockery is also a card that screams potential for a combo. I don't know what it is yet, but I wouldn't be surprised to see someone break this card.
I pretty sure most folk's first response to seeing Sarkhan Unbroken was to make some form of guttural grunt or yelp of satisfaction. Sarkhan has come a long way since Sarkhan Vol and Sarkhan the Mad. Heck, his most recent showing as Sarkhan the Dragonspeaker was pretty good, but this card blows them all away. Granted we are talking about a three color planeswalker, Nicol Bolas, Planeswalker was the first and previously only one, so Magic card design would somewhat dictate that he'd be good - the harder to cast the better it can be. Sarkhan Unbroken's major selling point is that he ticks off all the little boxes for being a good planeswalker. If your opponent has a board presence, you can tick him down and put a 4/4 dragon into play to protect him. This does leave him a little fragile, but you're probably still eating a creature with your 4/4 and absorbing a fair bit of damage if they are alpha attacking to finish him. If the board is empty and you're not worried about putting pressure on the game, you can simply +1 him for cards. Even if your opponent has a removal spell, you're still ahead on that exchange. These are the bread and butter interactions that make planeswalkers valuable. If Sarkhan Unbroken does have a weakness it's that the his ultimate isn't that good. You could certainly build a deck around maximizing it, but often the baseline for the truly great planeswalkers is that their ultimate can win the game on its own. Sarkhan Unbroken colors do lend itself to having dragons in your deck, but it's entirely likely to take over games simply by alternating his plus and minus abilities and never threaten the ultimate.