This thread contains a list of all the threads that can be useful for competitive play.
PokeMMO Official Usage Statistics and Tier lists
A Beginner's Guide to Building
OU Teambuilding Compendium
UU Teambuilding Compendium
NU Teambuilding Compendium
LC Teambuilding Compendium
Competitive Pokemon Guide for Doubles
Official PokeMMO List of Clauses
Barrage's Comprehensive Guide to Competit