I use a standard FWG core comprising of Heatran, Gastrodon and Celebi, and it has done me well so far. The set helps counter most weather and the threats that come with it. Heatran walls sun teams for the most part, while Gastrodon does a fair job dealing with rain teams. Celebi completes the core by adding a couple of crucial resistances to fighting and ground. Couple them with a stallbreaker and an offensive core that isn't very susceptible to passive damage, and you have a decent team in your hands.
The sets I use are pretty standard; stuff you can find on their analysis pages. Specially defensive heatran, Wall Gastrodon with a Tinkerbell Celebi. I'm considering making Celebi physically defensive though, as it would allow her to sponge hits from the likes of Terrakion and Breloom better, but I'm finding the power and utility in the tinkerbell set too good to pass up.
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