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Since most rain sweepers don't run max speed Ludicolo could surprise them by running max speed himself and hitting with STAB Grass attacks but is too slow to do much outside of rain.
For Crobat I've used 168 HP / 48 Atk / 156 Def / 136 Spe Jolly
Outspeeds Timid Starmie, always survives +2 Adamant Luke's ESpeed after rocks and has a good chance of OHKOing after a CC defence drop as well as always OHKOing Machamp with Brave Bird.