There are an increasingly large number of moves in Pokemon that will boost the stats of the user, making them tougher, faster, and more offensively powerful. These moves are popular- and with good reason. They can turn a tank into a hugely durable sweeper, a wall into a supertank, and they can even turn unremarkable pokemon into good pokemon of any variety or improve the function of a pokemon at what it already does- just consider Calm Mind Cresselia. At first it seems like these moves have no true counter- yes, it takes time to use them, but applied judiciously, there isn’t any actual drawback...
...or is there?
Enter one of the more interesting Dark-type attacks: Punishment. Punishment is an interesting attack with a variable power. When used on a pokemon most of the time, it will barely cause any damage. But if the target of Punishment has any stats boosted- including accuracy or evasion- then it starts inflating into something truly powerful.
Punishment’s power is variable, but it amounts to this- a power of 20 for each grade of stat boost on its target. If your opponent has used Calm Mind twice and you hit it with Punishment, you’re using a power-80 attack, nearly the equivalent of Crunch. Used against a serial-booster it’s not hard to reach a power of 120 or 140 with Punishment- the equivalent of Fire Blast or Blizzard, without the low accuracy. This would be dangerous enough to an opponent who is boosting anything other than their Defense.
Enter Swagger and Flatter, moves that confuse the opponent while boosting one of their stats two grades. Flatter is mostly an annoyance- boosted Special Attack isn’t going to do anything when you’re confused. Swagger is dangerous, though, granting a two-level boost to the target’s attack and confusing them- therefore increasing the damage they do when they hit themself. When you combine these with Flatter, however, things get really dangerous, and that 200-power cap on Flatter doesn’t look so far off.
The best thing about Punishment is that the pokemon that gain access to it almost all have access to Swagger or Flatter, and many of them are very quick, enabling them to use Punishment to take out things that they otherwise might have no business fighting. Most notably, one player used a Punishment-wielding Primeape, a pokemon usually consigned to the Underused Tier, as part of a team of Underused pokemon that destroyed teams built in the Ubers Tier, reserved for the most powerful Legendaries and a few of the truly abusive non-legendary pokemon.
Other notable Punishment users include: Slaking, Infernape, Arceus, Zoroark, Landorus, and Weavile (who can throw its own Swords Dance on top of Flattery for really severe abuse).