Take anything from RU or NU that you think should be more powerful but isn't used and then use that in a manner contrary to how it is used.
I had an idea for awhile of abusing Gardevoir with Trace and Choice Scarf. The idea being that many poke's weakness is their own ability (intimidate, flash fire, water absorb, lightning rod, ect), which when combined with trace would allow ample free switch-ins. Something like
Or whatever move I feel is necessary. I haven't done any calculations, but another option would be training into HP if speed is high enough, allowing more bulk and use as a special sponge. Not sure that would be work, though. Basically you use this to switch into special attackers or pokes with abilities that counter themselves, and then hit them quite hard right back.
The last move's unpredictability is where the advantage really comes in. The fact is, you are never sure just how much of a "scarfer" you are dealing with. You may be fighting a poke that will disable your sweepers. You may be fighting a poke that will suicide itself. You may be fighting a poke that does both, or a poke that does neither. You may not even be fighting a scarfer, given the frequent use of Gardevoir support sets. Until all moves are used, it is unpredictable.
Rest in Peace City of Heroes: April 27, 2004 - November 30, 2012. We will miss you. Cause of death: "Realignment of Company Focus" by NCsoft.
As someone who almost always uses giimmick for my team, I should say that gimmick only work when it can do something more than being a gimmick because its.... Welll a gimmick
For example here's a set I had sucess with
Drudiggon 252hp 252 atk 6 spd
Fire Fang Outrage Sucker Punch Superpower
This is essentialy mini Dragonite who works quite well during the early bw era where many still prefer Hippo, but Ttar is still quite prominent. This can beat ghost, some psychic thing, revenge kills, kills steel quite well, and back then it OHKO the common Toed
Not exactly a good example though(a better example would be like... Raptor or Zapdos)