I’ve heard a few people complain about the 4/4 and the fact that he’s in prime Mortars territory, but yeah. What card doesn’t have a vulnerability or two (Go away Thragtusk, you don’t count anymore)? We’re getting crazy-awesome value for 5 mana otherwise, and nobody is really complaining about a 4/4 flier for 5 in red anyway. I can’t think of a better way to top off the mana curve of an aggro deck than with this guy plopping down and making things silly.
Now, I wouldn’t bet on his monstrous ability to make it in a multiplayer game (those kinds of things generally tend to attract unwanted attention and cause a few unwanted, unfriendly alliances in a hurry), but in any sort of constructed standard format, you’re going to be smiling when he hits the table.
I know personally that a few LGS favorites, Azorius Charm, Detention Sphere, and Banisher Priest are shooting blanks at him. Have fun banishing my Goblin Diplomats while I fly over and deal 4, haha.
The thing about the dragon that we haven’t even gotten into yet is what I like to call the sleeper/finisher, monstrosity! Yes, it’s expensive, and yes, it’s going to be a huge problem for your opponent when you make this guy monstrous. It’s not likely that you’ll be dealing much direct damage, unless your opponent has some form of Esper/Control with good draw. Then you’re punishing him all the more. Just be mindful of his mana, and whether or not he has a response to your monstrous trigger. Stormbreath Dragon has to be on the battlefield when his ability resolves to actually trigger the ability.
Remember, you can use monstrosity any time you have the mana up, so look for a time when your opponent is tapped out/doesn’t have an answer in hand to use it. At the very least, it should stop your opponent from using any Sphinx’s Revelations while he’s out. Effectively wasting that card until he can deal with your dragon.