Eisenwald was an assassination guild and was the main antagonistic faction of the Lullaby Arc of the anime/manga series Fairy Tail. It was a dark guild that conducted assassination jobs and saught revenge against the Magic Council for supposedly taking away their freedom.
Eisenwald was founded at an unknown time by an unnamed master. Sometime prior to X784, the Magic Council had prohibitad wizards from doing assassinations and since Eisenwald had done that, the guild was kicked out of the Mage Guild League and was labled as a Dark Guild. At some point in time, their guild master was arrested and the guild was ordered to dissolve but it refused. Erigor would later on take over as Eisenwald's substitute leader in the abscence of their master.
The goal of Eisenwald was to get revenge against the Magic Council for taking away their freedom, "locking them up in the darkness" and ruining their lives. In order to accomplish this, Eisenwald had saught after the flute Lullaby to use against the Guild Masters at their anual meeting in an effort to kill all of them and throw the council into chaos dealing with rogue guilds. They eventially battled against Team Natsu of Fairy Tail which ultimately costed them their defeat and their guild was eventually disbanded.
Eisenwald was an assassination guild and had many specialized assassins in the guild. Despite this however, there was very few notably strong members of Eisenwald with the only exception being that of Erigor with his powerful Wind Magic. Other than that, most of the other members of Eisenwald are at a strength level of an average mage with Erza Scarlet being able to defeat many of them with ease.