Tiers are soon to be, excited? Anyways, This is PokemonDB's official Metagame rules.
Clauses
If you re on this page, you are likely a battler. Most of you should know these clauses, but we have some new ones. Plus a refresher never hurt. For those who do not know, clauses are universal rules to ever tier(w/ exceptions). They basically nerf out some annoying as hell strategies, such as using Spore on an entire team. We currently use Smogon's basic clauses, as well as 2 new ones. Get used to these, because they can cost you a match if you aren't up to speed.
Species Clause - A player cannot have two Pokemon with the same National Pokédex number on a team.
For example, using a team with two Koffing would break this clause.
Using different formes on the same team, such as Rotom-W and Rotom-C, also breaks the clause since they share the same Pokédex number (#479).
Sleep Clause - You lose if, at the end of your turn, two of your opponent's Pokemon were put to sleep by a move you used but were not forced into, and neither have had their sleep removed since then.
The clause basically means that if you have already put a Pokemon on your opponent's side to sleep and it is still sleeping, you can't put another one to sleep.
A move you were "forced into" is a move you must use because all other moves (that cannot inflict sleep) are disabled (by Choice item, Encore, or some combination of Taunt, Disable, Torment, and lack of PP) and you cannot switch (due to trapping moves, trapping abilities, Ingrain, or having all other Pokemon be fainted).
A move you used includes moves called by Metronome, Sleep Talk, Assist, Me First, or Copycat. It does not include Magic Coat or Magic Bounce.
Rest, used by either player, is never counted by this clause.
Evasion Clause - A Pokemon may not have the moves Double Team or Minimize in its moveset, nor plain accuracy lowering such as Sand Attack.
Generally, this rule will be automatically enforced in simulator play. In Wi-Fi play, a player is considered to have broken the clause when a Pokemon is revealed to have been brought into the battle with a banned move.
OHKO Clause - A Pokemon may not have the moves Fissure, Guillotine, Horn Drill, or Sheer Cold in its moveset.
Generally, this rule will be automatically enforced in simulator play. In Wi-Fi play, a player is considered to have broken the clause when a Pokemon is revealed to have been brought into the battle with a banned move.
Moody Clause - A team cannot have a Pokemon with the ability Moody.
Hazards Clause - Stealth Rock, Poison Spikes, and / or Spikes cannot be on the field together. This means Spikes cannot be used if Stealth Rock is up, vice versa.
Instant Abilities Clause - A team cannot use Drizzle, Drought, Sand Stream, or Snow Warning with the following abilities:
Sun: Chlorophyll, Flower Gift, Leaf Guard, and Solar Power.
Rain: Hydration and Swift Swim.
Sand: Sand Veil, Sand Force and Sand Rush.
Hail: Ice Body and Snow Cloak.
This clause does not apply in Ubers.
Tiers
What is a tier?
Tiers are the only real way to pick out the low from the weak, so everyone can have fun. Seeing 6 dragons vs. 6 Sunflora is just awful. If you do not understand how they work, think of it as the Square-Rectangle theory. A Square is a rectangle but not all rectangles are squares.
There are 5 primary tiers, being Ubers, OverUsed, UnderUsed, RarelyUsed, and NeverUsed. (There are also special Metagames such as NFE, Little Cup, and Clear Skies.) How do they work? Well, low tiers can be used in higher tiers, higher tiers cannot be in lower tiers! If you use a team of Bidoof, Patrat, Weedle, Pidgey, Starly, and Dialga, your team is classified as Ubers. You may not face people off in any other tier. If Dialga was instead a Politoed, your team would classified as OU. It can battle OU players and Ubers players. Get it? No matter what, the highest tiered Pokemon in a team makes it that tier. I'll make it simple.
Ubers: Any Pokemon can be used here!
OverUsed: Pokemon from any tier can go here, except Ubers. Also the most commonly played.
UnderUsed: Pokemon from any tier except OU and Ubers can play here.
RarelyUsed: Only RU and NU Pokemon can go here.
NeverUsed: Only Pokemon from this tier can go here!