Yes, this set is a bit weird, but it might turn out to something.
Gyardos/Mega Gyardos
@Power Herb/Garadosite
-Aqua Tail
-Outrage
-Iron Head/Dragon Dance*/Ice Fang
-Bounce*/Payback
The * means don't use this in the Mega-Evolution set. As stated before, this set is very gimmicky. From the outset, Aqua Tail is Gyrados' best STAB for water. Outrage is very powerful. Iron Head and Ice Fang are there for coverage, and Dragon Dance is a signature move on Gyardos sets, but don't use it on the Mega Evo set I'm giving. The last part is a bit odd. If your going for normal Gyardos set, the ability should be Moxie. Bounce and a Power Herb are the only way your going to get use out of Gyardos' Flying STAB. IF your running Mega Gyardos, the go for Payback, and don't use Dragon Dance. Payback, if used properly, could go from a lame 75 power to an outrageous (*ba dum tish*)150 attack power (please check). HOwever, that means neglecting speed IVs and EVs. But that shouldn't be too much of a problem.
So yeah, I might as well have given just a Mega-Gyardos set, because Bounce is useless after the first time using it. It's a bit odd, but it works. I use the Mega Evo set myself.