Mighty Nein

The Mighty Nein are an adventuring party and the protagonists of Critical Role in Campaign 2, starting with Chapter 9.

Meeting in Trostenwald
The seven individuals who would become the Mighty Nein first met in Trostenwald in 835 PD. Up to that point, they had been traveling in three groups:
 * Caleb and Nott helped each other break out of prison about five or six months prior, and had since been traveling and pulling cons together.
 * Jester and Fjord had met in Port Damali before running into Beauregard not long afterward. They were heading toward the Soltryce Academy.
 * Mollymauk and Yasha were members of a carnival that had just arrived in town.

Caleb, Nott, Jester, Fjord, and Beau all happened to be staying at the Nestled Nook Inn, where Molly and Yasha came to advertise their carnival. Later, when the carnival turned suddenly violent, the seven of them worked together to defeat an undead menace and became embroiled in a local investigation. They formed an alliance to clear their own names, then chose to travel together afterward.

Yasha alone did not leave Trostenwald with the rest of the group, and was prone to disappearing on her own business for stretches of time. However, the group made a point of meeting up with her when they could. (Out of character, Yasha's absences were due to Ashley Johnson's frequent scheduling conflicts.)

Name
Upon defeating a gnoll pack that had raided the town of Alfield, the adventurers earned some renown for themselves. The local watchmaster, Bryce Feelid, asked for a group name for their Crownsguard paperwork. After conferring among themselves, the group settled on The Mighty Nein, a nod to Caleb's Zemnian accent.

From an out-of-character context, Liam O'Brien had been using German words and a German accent as a stand-in for Caleb's Zemnian. The rest of the cast picked up on this and would yell "Nein!", the German word for "no", whenever a nine was rolled or referenced. The joke became a running gag over several episodes. When asked to come up with a group name on the spot, nein was the first thing the group landed on, plus mighty for strength.

Trivia

 * The name may also be a reference to the 2016 video game "Mighty No. 9", whose voice cast included Matthew Mercer as Pyrogen (Mighty No. 1), Steve Blum as Countershade (Mighty No. 8), and Yuri Lowenthal as Beck (Mighty No. 9).
 * There are nine members of the adventuring party when Frumpkin, Yasha, and Jester's Invoke Duplicity self are counted.
 * Yasha is not formally a member of the Mighty Nein, as Ashley Johnson was absent when the adventuring party was officially founded.