I have a weird idea that I haven't had time to test, but the numbers look promising-ish. I'll post it in my next RMT if it doesn't suck.
Porygon Z @ Chople Berry
Modest - Download
252 HP / 144 Defense / 104 Special Defense / 8 Special Attack
Tri-Attack
Shadow Ball
HP Fighting / Charge Beam
Recover
A common misconception is that Porygon Z is incredibly frail, when in reality its actually bulkier than Starmie and has just one weakness. The key to this set is Download and Recover. Download gives me a Special Attack boost when the defending pokemon has less Special Defense than physical. Zapdos, Swampert, Vaporeon (when Bold), Scizor, Skarmory etc. Most of the metagame is physically defensive, even mixed sweepers run Rash and Naive to avoid the physical hits they would take. When defensive stats are tied, I get a Special Attack boost by default (Lucario, Heatran, Kingdra, some Infernape etc).
I'm feeling lazy so I'll make this quick. Downloaded Tri-Attack will 2HKO Swampert while the other moves round off the coverage. Shadow Ball will beat Celebi while HP Fighting kills Heatran, Tyranitar and even physical Skarmory. The Special Attack isn't truly massive, but its still enough to OHKO frail pokes like Infernape and 2HKO bulky things. In other words, it does what it has to. Downloaded Tri-Attack hits harder than Mixape's LO Close Combat!
Porygon Z can take retaliatory hits fairly well. It is guarenteed survival against Choice Band Tyranitar Stone Edge, +1 LO Gyarados Waterfall, LO Infernape and Heatran Fire Blasts, Gengar Focus Blast and even +0 LO Lucario Close Combat AFTER Stealth Rocks. Obviously this will put Porygon Z near death but he is capable of OHKOing all of them back (with a download boost and in Heatran's case, 20% prior damage). This is nice in a pinch, but the reason for Recover is Porygon Z's fantastic ability to be 3-4HKOed by just about every bulky pokemon around. Celebi, Swampert, Skarmory, Zapdos, Vaporeon, Impish Skarmory, Spinner Starmie, Gliscor, Hippowdon, Cresselia, Magnezone, and Rotom all fail to 2HKO Porygon Z while you happily KO them back in one or two shots (even Cresselia is 2HKOed) Recover stalling when needed.
Porygon Z can 1-2HKO most of the metagame with almost no fear of a retaliatory OHKO from big sweepers while weaker walls barely break 30%.
EH?
**Charge Beam is an option to beat Blissey with (sort of) and also take on Specially Defensive Skarmory. Charge Beam will also bring Tri-Attacks power beyond anything else seen in OU after one boost, but at the cost of coverage (you can drop Shadow Ball too).
