Well if you want a rain abuser, why not the ones banished to Ubers for being too powerful in rain?
Thundurus@Life Orb
Ability: Prankster
EVs: 4 hp 252 sp atk 252 spd
Timid Nature
-Nasty Plot
-Thunder
-Hidden Power Ice
-Focus Blast/Grass Knot
Prankster is an absolute godsend for about any Pokemon (see Sableye) and for Thundurus is no different. A practically guaranteed Nasty Plot is no laughing matter. Thundurus's good base 125 sp atk in coherence with its awesome base 111 speed means that it hits hard and fast, and it doesn't hurt to have a ludicrously powerful STAB in Thunder to back it. Then add near perfect coverage in HP ice, augmented by even more great coverage in grass knot or thunder and you got youself an awesome rain sweeper, even in the Uber tier, and definately an overpowered sweeper in Ou.
Tornadus-T@Choice Specs
Ability: Regenerator
EVs: 4 hp 252 sp atk 252 spd
Timid/Naive Nature
-Hurricane
-Focus Blast
-Heat Wave/Hidden Power Ice
-Air Slash/U-turn
Another member of the kami trio with a ridiculously awesome ability that can fire off powerful special attacks. At base 110, its special attack is somewhat low for ubers, so choice specs fixes that. Also, hurricane is so ridiculously powerful that it does not matter. Focus Blast provides great required coverage, so it comes in in the next slot. Heat Wave is weakened by rain, but sometimes the rain isn't up and there's a steel type standing in your way, and HP ice is useful with the multitude of flying and dragon types in Ubers. Air Slash is a weaker, more reliable STAB, and U-turn facilitates switching, and by extension, prediction and regenerator recovery.