You can only get TM87 Swagger by paying 36 Battle Points (BP) at the Exchange Service Corner within the Battle Subway. The Battle Subway is located in the center of Nimbasa City.
The Battle Subway has seven subway trains that hold a different style of battle. BP gets awarded to you based on win streaks and the difficulty of each battle you win.
TMs and other battle items can be purchased with BP at the Exchange Service Corner on each subway.
As for the move itself:
Swagger is a non-damaging move that inflicts Confusion upon its target at the expense of also raising its Attack stat by two stages.
TM87 Swagger Location (Step-by-Step)
Step 1: Starting at the Nimbasa City Pokémon Center, head east towards the center of the city.
Step 2: The large building east of the Pokémon Center is the Battle Subway. Enter the building.
Step 3: The entrance to the Battle Subway leads to a platform with seven subway trains.
Enter any subway you’d like – they all have an Exchange Service Corner.
Step 4: After entering the subway, you’ll see the Exchange Service Corner in the northwest corner. Talk to the clerk on the left.
Step 5: TM87 Swagger can be purchased from the clerk here for 36BP.
Along with TM87 Swagger, the clerk also sells the following TMs:
|TM23 Smack Down||36BP|
|TM34 Sludge Wave||48BP|
|TM51 Ally Switch||48BP|
|TM77 Psych Up||48BP|
Swagger Details + Uses
|Swagger Move Details|
Swagger is a Normal-type Status move that confuses its target, while also raising the target’s Attack stat by two stages.
This effectively doubles the target’s Attack, making your opponent much more deadly.
But with that said:
Confusion is a frustrating status condition to deal with. It can last anywhere from 2 to 5 turns, and has a 50% chance each turn of causing the target to hurt itself in confusion. The damage from these self-inflicted confusion hits come with a base Power of 40.
Swagger is frequently used with the move Foul Play, which is an attack that inflicts damage based on the Attack stat of the target as opposed to the user.
When used after Swagger, Foul Play becomes a supercharged attack with double the Power and very few drawbacks.
In fact, the combo of Swagger and Foul Play became banned in competitive play due to it being so overpowered.
That being said, there’s nothing preventing you from using this combo during a single-player game of Black or White. So if you have the BP and the right team setup, this can be a great higher-level move combo to look into.