Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
Well idk about Meganium but I know Ludicolo should be Adamant (SD, Waterfall, Seed Bomb, Rain Dance)
And Meganium I would say Adamant because its attack is already really low ;_;