Well, like Generekt said, Gren's now in Ubers. Ubers is filled with hyper-bulky Pokemon like Giratina and Lugia, and hyper-powerful pokes like Mega Mence (take THAT Zard X) and Primal Groudon. (And then there's Mega Rayquaza.) I believe that hyper offense is more common in Ubers, and since Gren is so fast, the Pokemon that switches in is gonna take a hecka powerful Attack. Gren needs to keep up with the power, and so only opts for powerful moves like Hydro Pump and Gunk Shot.