The key difference between the abilities of Mirrorwing Dragon and Zada, is that Mirrorwing can copy any spell that targets it. However, don't worry about a removal spell wiping out your whole board. That spell is copied by the player casting it and affects the creatures on his or her board, not yours. While this can certainly backfire, played correctly, there is so much potential to be realized. Many EDH / Commander players found this out.
The most obvious home for Mirrorwing Dragon is in a Zada, Hedron Grinder deck. Mono-Red has plenty of pump spells such as Brute Force, Run Amok, Temur Battle Rage, and Titan's Strength. Chandra's Ignition is particularly potent and Mirrorwing makes a good alternate target to Zada. While Ignition will wipe out all of your creatures including the Dragon itself, your opponents are likely going to be dead, as well.
Essentially, Mirrorwing Dragon just becomes a second copy of Zada. The big difference is that Mirrorwing isn't open to targeted removal in the way that Zada is, which is pretty nifty. People don't usually want to wipe out their entire creature lineup to deal with a non-Commander. It's a really good fit alongside Zada and it can help you win the game without Zada in play.
Unfortunately, there is no infinite combo between Zada and Mirrorwing Dragon targeting each other infinitely. This is because their abilities only occur when the spell is actually cast, and not copied.
There isn't really a great fit between Mirrorwing's ability and Scion Dragon Tribal decks. The only real advantage to including Mirrorwing Dragon in a Scion deck is that he's a bit tricky to kill. Being able to put Mirrorwing Dragon in the graveyard at instant speed to make your opponent's targeted removal backfire is a cute trick, though. I'd include Mirrorwing just for this corner case scenario, honestly.
Unfortunately, the copies of spells that Mirrorwing Dragon creates do not trigger Prowess. However, this doesn't mean that Mirrorwing Dragon isn't excellent alongside the ultimate Prowess Commander, Shu Yun, the Silent Tempest. In fact, Mirrorwing is a great companion to not only Shu Yun himself, but his companion creatures such as Monastery Mentor (and his Monk Tokens), Talrand, Sky Summoner (and his Bird Tokens), and Young Pyromancer (and his Elemental Tokens).
The Kaladesh Enchantment Metallurgic Summons is also a great include in the Shu Yun deck, and the Mirrorwing Dragon plays nicely with the Construct tokens it creates. Shu Yun decks also play Rite of Replication, which copies (along with its kicker) for each creature you control. Talk about taking over the board!
Another great place for Mirrorwing Dragon is EDH is in Atarka, World Render decks. It's a solid inclusion in some builds of Atarka that cast pump spells like Stonewood Invocation, which gives a creature +5/+5 and hexproof until end of turn. If your Dragons are already getting double strike from Atarka's ability, chances are you're very close to winning the game. Become Immense is particularly nasty with Mirrorwing, also. Plus, casting Hunter's Insight on Mirrorwing while you have a few other Dragons out means you'll be drawing a nice amount of cards.
There's also the Mirrorwing Dragon combo with the Wolf Silverfur Partisan. While it hasn't really become a combo in Commander, it was a fun Standard deck. Basically, the Partisan creates a 2/2 Wolf Token each time a Wolf or Werewolf is targeted by a spell. Because Mirrorwing Dragon copies spells to target each of your creatures, you end up creating a whole bunch of Wolf tokens. There was a Red/Green Standard deck that played Zada , Mirrorwing, and Partisan that could steal some wins. But this combo isn't possible in a Zada deck, being that Silverfur Partisan is green. It's technically possible in Commander, but it would go best built it into an Ulrich of the Krallenhorde Werewolf Tribal deck and Mirrorwing Dragon would feel awfully out of place.
Mirrorwing Dragon and Heroic
You may have heard of players building Heroic-themed decks around Anax and Cymede and including Mirrorwing Dragon. Unfortunately, Heroic is a mechanic that only triggers on cast. So, although the copies of spells made by Mirrorwing Dragon target, your Heroic creatures won't have their abilities activated. However, despite this fact, people will include Mirrorwing Dragon anyway. There are times where you'll cast a pump spell that's so potent in certain board-states that Mirrorwing Dragon (or Zada for that matter) will actually help you win the game without even needing to trigger Heroic. So, there actually is synergy between the Heroic strategy and Mirrorwing Dragon, although not with the Heroic cards themselves.
As time goes on, Mirrorwing Dragon will probably find its way into even more EDH decks. It makes for a powerful complementary piece to "go wide" strategies complemented by powerful targeted instants and sorceries. While it may never make waves in Standard or Modern, it will definitely be a Dragon to watch out for in EDH for years to come.