Apparently, this is the optimal competitive set on Showdown:-

Serperior @ Life Orb
Timid Nature
IVs: 29 HP (all others standard - this spread decreases the damage from your LO)
252 SpA/4 SpD/252 Spe
Leaf Storm
Dragon Pulse
Hidden Power Fire
Giga Drain

There are arguments to be made for Glare, Taunt, and Synthesis in that last slot, but a boosted Giga Drain can heal a lot and still do decent damage. Dragon Pulse is there for coverage and HP Fire is the way to go - there are arguments for HP Ground, chief among them being Heatran, but Fire hits more stuff harder, like Scizor and Ferrothorn. It has a simple function, that being Leaf Spam and its inbuilt Nasty Plot, and it's effective in OU, especially because of its ability to outspeed common threats unboosted - and since it can't boost its speed because Contrary, that's an important thing to remember.

Its bulk ain't great and sometimes it fails in its duty to OHKO bulky Water-types (though Mega Swampert gets rekt), but there's quite a lot to like about Serperior. Hopefully its inevitable Mega retains Contrary and a halfway-decent secondary typing. It'd be interesting for it to get, say, Dragon-type and have it be some kind of Eastern wyrm-lookin' thing, and it'd fit in with the regal theme it's got going on - plus, Dragon Pulse is about the only proper coverage move it has, so, y'know, there's that. Ground-type would also be interesting if it got some proper coverage, though that nasty 4x weakness to Flying is unpleasant in a tier with Talonflame in it.

Please accept my apologies: Serperior is superior, and I was wrong to assert otherwise. =]

Its special movepool is basically Grass and Dragon, and because Dragons are kind of going out of style thanks to the aforementioned Fairy type, without STAB to make those moves more effective, its special coverage potential is pretty abysmal. Contrary does somewhat make up for this, of course (a Leaf Storm-Boosted Hidden Power can be pretty devastating) but the lack of stronger coverage moves hurts pretty badly. That said, the physical movepool is so much more promising, boasting the likes of Aqua Tail, Outrage and Knock Off. With Coil, it could even perhaps make Iron Tail work. If they added Superpower or Horn Leech to the mix (unlikely though that is), Physical Serperior might actually have some presence.

All that said, I may have to concede that my beloved Support Serperior no longer works in this generation. In fact, my entire Grass mono seems hopelessly, utterly outmatched. It's going to take some major tweaking to get them back in working order.