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Hey, I would really consider going back to Ludicolo with Swift Swim and Rain Dance over the Venusaur.
Also, I have a currently undefeated Rain Dance mono-type team. My lead is the most unusual lead. I use the Swift Swim Sweeper set as the lead with Focus Sash. Always gets rain started and...
I like the suggestion of Flygon except for the fact it sort of brings away the whole theme of bulky sweeping and still leaves me weak to special sweepers. I will be testing Flygon out.
All but the Starmie suggestion I like due to the electric weakness. I had Latias in mainly for its defensive ability and it was able to fit in good with most of my team.