Re: If you had to bring in the REAL Mandarin how would you do it?
I'd have it revealed that the Mandarin didn't die in the explosion at the end of IM3, but the husk of body that survived was slowly rebuilt by Extremis. He realizes that he must bide his time and gather his resources.
Slowly, but surely, he amasses a wealth of technology...much of it alien in origin. Trevor's guise being Killian's idea in the first place, he comes to don the green dragon robe that inspired so much fear in those televised threats. He also decides to adopt the rings, but infuses them with some of the alien tech that he reversed engineered (perhaps they aren't just simple rings, but more like techno-brass knuckles with wires running from them up his arm and then under his skin, powered by his Extremis energy). He wants to the world to know that the threat of the Mandarin was no hoax perpetrated by a drunken actor...it is very real and very dangerous.
Then he would seek out Tony to finish the fight he started.