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An Introduction to Smogon's Tier System
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<p>Smogon's tier system is used to rank Pokemon into several groups based on their perceived power and usage in competitive play. These tiers dictate which Pokemon can be used in the various metagames of competitive play. Each metagame encompasses different Pokemon, and therefore each one is unique in its style of play. The standards set by Smogon's tier system seek to balance competitive battling, ensuring no Pokemon is "too powerful" or over-centralizes the metagame it appears in. This allows players the flexibility to show "flair" in their team design rather than being restricted to using a particular Pokemon to win.</p>
<p>A Pokemon's placement within a tier is by no means set in stone. As people continue to engage in competitive battles, new strategies and movesets arise that may have previously been overlooked. Through increased play testing, the popularity of some Pokemon may fluctuate. Furthermore, the community may find their strengths and weaknesses to be handled by the metagame differently. Examples of what would prompt a Pokemon's change in tier include the adoption of new competitive movesets or the reduction in use of its counters. With this in mind, the Smogon tier system is reviewed and updated regularly to reflect how specific Pokemon are utilized by our community.</p>
<h2>An Overview of the Tiers</h2>
<p>Smogon has established five clearly defined tiers. Metagames restricted to a particular tier automatically include Pokemon from lower tiers. In practice, this means that in OU play, Pokemon from the BL, UU and NU tiers are allowed to participate, but Ubers are not.</p>
<h3>Uber</h3>
<p>The Uber tier is based solely on the power of the Pokemon present within it. Pokemon in this tier are considered to be too powerful to participate in the standard metagame. Note that no Pokemon is banned from competing with those in the Uber tier. The result is a "free-for-all" metagame with no restrictions on which Pokemon may participate.</p>
<ul>
<li><a href="/dp/tiers/uber">The DP Uber Tier</a></li>
<li><a href="/rs/tiers/uber">The RS Uber Tier</a></li>
<li><a href="/gs/tiers/uber">The GS Uber Tier</a></li>
<li><a href="/rb/tiers/uber">The RB Uber Tier</a></li>
</ul>
<h3>Over Used (OU)</h3>
<p>OU consists of the Pokemon used prevalently by our community. Since these Pokemon are used frequently, they can be deemed to have a strong combination of stats, typing, ability and movepool, as competitive battlers use them with the intent of winning their battles. All Pokemon present in the OU tier (as well as those present in lower tiers) may participate in what is our standard metagame.</p>
<ul>
<li><a href="/dp/tiers/ou">The DP OU Tier</a></li>
<li><a href="/rs/tiers/ou">The RS OU Tier</a></li>
<li><a href="/gs/tiers/ou">The GS OU Tier</a></li>
<li><a href="/rb/tiers/ou">The RB OU Tier</a></li>
</ul>
<h4>The Construction of the OU Tier</h4>
<p>For RB, GS and RS, the OU tier is formed based on the experience of our community in regards to which Pokemon are commonly used in Smogon's standard metagame tournaments. In tournaments, people use Pokemon that can compete at the highest level to allow them to win, so naturally they are an excellent means of determining the OU tier.</p>
<p>The OU tier for DP is constructed from the league statistics extracted from the current DP Pokemon battling medium. These statistics provide the number of times each Pokemon was used in the standard metagame league during each month, and those of the six months prior to the OU tier creation are utilised in particular to predict which Pokemon are going to be used in the near future. The Pokemon commonly used by expert players, who are highly-ranked in the league, receive heavier weighting than those used by less expert ones. Since, compared to the previous three generations, the DP standard metagame is still in its infancy, the OU tier for DP is continually updated on a three-month basis.</p>
<p>Shoddy Battle's weighted Pokemon usages lists of the six months prior to the OU update are first extracted from their website. The weighted usage of a Pokemon is the summation of the rankings of every player that used that Pokemon. For example, say both Blissey and Celebi are used three times during a day, and say that the players using Blissey had ranking 1650, 1360 and 1470, while those using Celebi had ranking 1520, 1360 and 1190. Their weighted usage for that day would be 4480 for Blissey and 4070 for Celebi. This would rank Blissey above Celebi in the weighted usage list, even though they were both used the same number of times during that day.</p>
<p>Each weighted usage of each month is then divided by the total of the weighted usages during that particular month, so that the probability of that particular Pokemon being used during that month is obtained. Suppose the probability for a particular Pokemon to be used in month m is <var>P_m</var>. These months are ordered in the following manner: if the list is being updated in July, then January, February, March, April, May and June correspond to months 1 to 6 in that order.</p>
<p>For each Pokemon, the predicted probability <var>P</var> is calculated as per the equation below, found using linear extrapolation techniques:</p>
<pre><var>P</var> = (50×<var>P_6</var> - 5×<var>P_5</var> - 4×<var>P_4</var> - 3×<var>P_3</var> - 2×<var>P_2</var> - <var>P_1</var>) ÷ 35</pre>
<p>These predicted probabilities are then sorted in descending order and made into a cumulative frequency, so that the 30th number, say, would be the probability that one of the top 30 used Pokemon is used in battle. Finally, the OU list is made to consist of all the Pokemon whose cumulative probability of being used does not exceed 0.75. This would mean that, whenever a Pokemon shows up in a battle for the first time, it has a 75% chance of being a member of the OU tier.</p>
<p>It can be shown that the probabilities of the usage of each Pokemon follow an exponential distribution. This means that the <var>n</var>th most used Pokemon will roughly have a <var>b</var> × exp(-<var>b</var>×<var>n</var>) probability of being used, where <var>b</var> is a constant that determines the shape of the exponential curve. The best value of <var>b</var> can be found using regression analysis on a spreadsheet program like Microsoft Excel. For Pokemon usages, it usually results in a value between 0.026 and 0.028.</p>
<p>In addition, the cumulative exponential distribution can be found using integration to be 1-exp(-<var>b</var>×<var>n</var>). This means that the probability that a Pokemon used in battle is among the first <var>n</var> most used Pokemon is 1-exp(-<var>b</var>×<var>n</var>). Thus, we can effectively solve the equation 1-exp(-<var>b</var>×<var>n</var>) = 0.75 to find the number of Pokemon that the OU tier will roughly contain in terms of <var>b</var>:</p>
<pre>
1 - exp(-<var>b</var> × <var>n</var>) = 0.75
exp(-<var>b</var> × <var>n</var>) = 1 - 0.75
exp(-<var>b</var> × <var>n</var>) = 0.25
-<var>b</var> × <var>n</var> = ln(0.25)
-<var>b</var> × <var>n</var> = -1.386
<var>b</var> × <var>n</var> = 1.386
<strong><var>n</var> = 1.386 ÷ <var>b</var></strong>
</pre>
<p>Assuming that <var>b</var> is between 0.026 and 0.028, the number of Pokemon in the OU tier would roughly contain between 1.386 ÷ 0.026 and 1.386 ÷ 0.028 Pokemon, or approximately 50 Pokemon.</p>
<h3>Borderline (BL)</h3>
<p>Pokemon in the BL tier aren't used enough to be OU, but bring imbalance to the UU tier. A BL Pokemon isn't necessarily weaker than an OU Pokemon. BL Pokemon, however, are used less for reasons such as requiring additional team support or simply being outclassed by another Pokemon in a specific role. It usually takes only one such inadequacy to explain why a given pokemon is BL and not OU.</p>
<ul>
<li><a href="/dp/tiers/bl">The DP BL Tier</a></li>
<li><a href="/rs/tiers/bl">The RS BL Tier</a></li>
<li><a href="/gs/tiers/bl">The GS BL Tier</a></li>
<li><a href="/rb/tiers/bl">The RB BL Tier</a></li>
</ul>
<h3>Under Used (UU)</h3>
<p>Pokemon in the UU tier are, put simply, underused. That is, when battling in the OU metagame, they will not be seen as much, likely because they are too weak. This weakness is judged based on a combination of stats, typing, movepool, and ability that restricts effective use of those particular Pokemon in the standard metagame. In UU play, Pokemon above the UU tier are banned, meaning NU Pokemon are still allowed to participate.</p>
<ul>
<li><a href="/dp/tiers/uu">The DP UU Tier</a></li>
<li><a href="/rs/tiers/uu">The RS UU Tier</a></li>
<li><a href="/gs/tiers/uu">The GS UU Tier</a></li>
<li><a href="/rb/tiers/uu">The RB UU Tier</a></li>
</ul>
<h3>Never Used (NU)</h3>
<p>Pokemon present in the NU tier lack qualities that would allow them to operate effectively, even in the UU environment. This is generally due to a combination of poor base stats, typing, ability and movepool. In NU play, only Pokemon in the NU tier are allowed. The NU tier attempts to place the Pokemon allowed within it on a more equal footing, allowing them to be used without the worry of being overpowered or outclassed by Pokemon in higher tiers.
<ul>
<li><a href="/dp/tiers/nu">The DP NU Tier</a></li>
<li><a href="/rs/tiers/nu">The RS NU Tier</a></li>
<li><a href="/gs/tiers/nu">The GS NU Tier</a></li>
<li><a href="/rb/tiers/nu">The RB NU Tier</a></li>
</ul>
