Managed to complete this after 400-500g repair. My ilvl was 514 and mostly LFR-valor geared.
Tried all specs and definitively MM was the best by far for me. Adds were the most difficult to handle but Thrill of the Hunt is also a must talent. Kited then in small circles taking advantage of ice and explosive traps.
I also used no pet because to me I felt it was mostly messing adds kiting than helping.
What worked great to me as well was to kite and kill adds asap and in mid room and rush to platform behind dragon. When adds revived and until they got there, Wrathion was gone to make his clone phase and I could "finish" adds easily.
Yet I have the impression the event is quite bugged: 1) When adds were back, a couple of them get their health stuck at 1% but kept chasing me. I had to FD so they returned to mid-room and stopped chasing; 2) I am pretty sure I did little to NONE damage on clones/real Wrathion. When I FD to reset the adds, clone phase just ended by itself and I could finish Wrathion on the platform.