Monsoon

I think it has to be clear weather and you'll need pokesnax for it now, too.

If you really need another member, maybe you could go for Zoroark, it massacred his entire team for me :3 But your team should be able to handle Radomus.

For me it was Serra because I would have so much bad luck with freeze hax and missing. I had to get the Vulpix for the Drought so I could actually hit her Pokemon and make Blizzard miss. I destroyed Florinia actually because I had a Charmeleon with Dragon Rage and Golbat which made Cradily really easy to defeat.