Standard/Overused (OU)
Standard, as it implies, is the general and 'normal' environment for
Competitive Pokémon Battling. Ubers are banned from this environment
but everything else is okay. This is where most people battle and the
likes of Salamence, Garchomp, Tyranitar and Blissey can freely be
used. The term 'Overused' is also used for this environment, since
this is where the most frequently used Pokémon will battle.
Standard, Borderline, Underused and Neverused Pokémon are all freely
accepted in this environment.
Underused (UU)
As the name implies, this is where Pokémon who aren't used often are
battled. Generally speaking, Pokémon in this environment are 'weaker'
than Standard Pokémon, and so this environment is used to battle them.
By limiting this environment it allows for a balanced Metagame whilst
granting a different experience to standard play. Pokémon like Altaria
and Flareon make their home here.
Underused and Neverused Pokémon are freely accepted in this
environment.
Never used (NU)
Pokémon in this environment are strictly speaking, the bottom of the
barrel. These include Pokémon who aren't even used in the UU
environment and the Metagame is considered somewhat of a novelty.
Pokémon like Beautifly and Luvdisc exist here. Only Neverused Pokémon
are accepted in this environment.
Borderline (BL)
Borderline is the home for Pokémon who are deemed too powerful for the
UU environment. Generally speaking, Borderline doesn't have a true
battling Metagame, rather its where 'Underused standards' are placed.
Examples include Pokémon like Articuno and Entei, their power is
clearly too strong for UU but they are rarely seen on Standard teams.
Were a proper Metagame for BL to exist: Borderline, Underused and
Neverused Pokémon would be accepted in this environment.
Uber
Pokémon placed in the Uber environment are Pokémon deemed too powerful
to be played in Standard. Generally their power is unbalancing, and if
they were allowed in standard play they would over-centralise teams
and limit the Metagame.
The following Pokémon are considered 'Uber' and are banned from
standard play:
Mewtwo Mew Ho-oh Lugia Latias Latios Kyogre Groudon Rayquaza Deoxys
(all forms) Dialga Palkia Giratina Darkrai Arceus Manaphy Wobbuffet
Some have called into question why Pokémon like: Jirachi, Celebi and
Shaymin aren't on this list, especially when: the Lati twins, Manaphy,
Deoxys and Mew are. The simple reason is because those Pokémon have
power comparable to most Standard Pokémon, whilst the Lati twins,
Manaphy, Deoxys and Mew don't.
Jirachi and Shaymin are limited by their shallow and predictable move
pools whilst Celebi is limited by a horrible typing. When compared to
Standard Pokémon they are balanced and as a result are allowed in the
Standard battling environment.
The Lati Twins on the other hand have fantastic typing, a good trait
and a great move pool, whilst Mew and Deoxys have unquestioned
versatility and fantastic offensive (or defensive) prowess. Manaphy,
despite having a fairly shallow move-pool, is near unstoppable with a
Tail Glow under its belt. When compared to Standard Pokémon they are
unbalanced and as a result are not allowed in the Standard battling
environment.
A lot of people also question why Wobbuffet is on this list. To put it
simply, its Trait combined with its stats make it too devastating to
be used in the Standard environment. This may or may not be changed at
a future stage, but as it currently stands, Wobbuffet is likely to be
locked into Ubers.
As you can guess, all Pokémon are freely accepted in the Uber
environment.
