League of Villains

The Villain Alliance (敵連合) is a group of organized villains that is made up of weak and powerful villains are the main antagonists of the series. The creator of the alliance is Sensei, with Tomura being the leader of the alliance while Black Mist acts as the second in command of the alliance. The mission of the Villain Alliance is to murder All Might.

History
The size of the Villain Alliance is estimated to be 75 (however, after the events at the USJ, the size of the alliance is dramatically decreased due to the majority of the villains belonging to the alliance along with Noumu being captured and detained by the Police). However, after Stain's defeat and capture, many villains inspired by him (such as Himiko and Dabi) sought out the Villain Alliance to join it since the organization was believed to harbor Stain's ideology; thus the Villain Alliance has increased in numbers.

Ultimate Space & Jams Arc
The Villain Alliance attacked the USJ in an attempt to kill All Might. However, the majority of the Villain Alliance (except for Tomura, Black Mist and Noumu) are defeated by Class 1-A. After All Might arrives, Noumu engages All Might in battle and is defeated.Tomura and Black Mist try to finish what Noumu started but their attempt is thwarted by Izuku Midoriya and the timely arrival of the Yuuei Pro Heroes. Both Tomura and Black Mist are sucked into a Black Hole created by No. 13 (However, Black Mist creates a portal back to their hideout, teleporting themselves out of harm's way). Thus, the Villain Alliance is defeated and the majority of the villains of the alliance (along with Noumu) are captured and detained by the police, leaving Tomura and Black Mist as the only remnants of the Villain Alliance.

Sports Festival Arc
During the Yuuei Sports Festival, Black Mist sought out the Hero Killer, Stain, due to his notoriety. Black Mist manages to find Stain and asks for a moment of his time, teleporting himself and Stain away. Stain meets with Tomura in order to test his evil. Afterwards, Black Mist teleports himself, Stain and Tomura to Hosu. While Stain goes off to finish his business, Tomura decides to humiliate the Hero Killer (as he got on his nerves) and sends three Noumus to attack Hosu. The Noumus fight the Pro Heroes and give them a hassle, as well as cause chaos and destruction along the way. By the time Izuku, Shouto and Tenya apprehend Stain, two of the three Noumus are restrained and arrested by the Pro Heroes and Police Force while the other Noumu is killed by Stain. Tomura, annoyed that nothing went his way, decides to head back to the Villain Alliance hideout. Black Mist and Tomura leave Hosu.

End of Term Test Arc
After Stain's defeat, the media credits the Villain Alliance as an organization that harbors and carries out Stain's ideology. As a result, many newcomer villains who were inspired by Stain's ideology have sought out the Villain Alliance in order to join it, causing the Villain Alliance to gain spotlight and notoriety. Two villains, also inspired by Stain's ideology, attempt to join the Villain Alliance so that they can be with the organization Stain was believed to be apart of, after being scouted by a broker (who decided to take advantage of the Villain Alliance's new notoriety) in order to earn more money. However, the meeting between Tomura and the two potential candidates does not go well. Black Mist asks the broker to wait a few days for their reply regarding Dabi and Himiko's registration into the Villain's Alliance. They eventually join and become part of the Vanguard Action Squad.