BL pokemon are banned from UU due to being too strong in that tier(by vote), but are not used enough to classify as overused
BL2 pokemon are banned from RU and are not used enough to classify as Underused
Other than bans, the bottom 6%(or less) in the above tier is used to determine a pokemon's placement. So that the UU pokemon are used on <6% of OU teams; RU pokemon on <6% of uu teams; and NU pokemon on <6% of RU teams. Overused pokemon are used more than 6% in the tier Overused. Of course they don't refresh the tiers quite as often as gamefreak releases new stuff....
The reason for all the tiers is so that pokemon that cannot fight against stronger ones will have an enviroment where they will be useful. Naturally you are allowed to use any pokemon in the tier below the one you are playing, but keep in mind that there is a reason its not used as much. I.E. uu pokemons are allowed in OU matches, NU in any match, and RU are allowed anywhere but NU.
Last edited by carrot rust; 3rd October 2012 at 11:17 PM.
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