Mustache Pirates

The Mustache Pirates was a pirate crew in the sixth One Piece movie. It was headed by Brief.

Past
The Mustache Pirates came to Omatsuri Island; however, everyone except for Brief was killed by Lily Carnation.

Baron Omatsuri and the Secret Island
When Monkey D. Luffy and his crew arrived on the island, Brief watched them from a distance and later got Luffy alone where he offered him to join the Mustache Pirates and defeat Omatsuri. Luffy declined, but Brief warned him about Omatsuri.

Later, he saved Luffy from being killed by Omatsuri. Together, the two partnered up to distract and defeat Omatsuri, with the help of Papa and the Tearoom Pirates, the former of which who actually killed Lily Carnation. At the end of the movie, Brief acknowledged that he would remember Luffy and would look for a new crew, inspired by the young captain.

Jolly Roger
The Mustache Pirates Jolly Roger was a skull with a toothbrush-mustache and a hat, matching the crew's uniform appearance.

Crew Members
The only named member of the crew is the captain, Brief. Including him, each of the crew members had the same kind of mustache, but none of the others were ever seen except in a photo.

Later, Brief asked Luffy to join his crew. Luffy declined, saying he had his own crew, but, at the end of the movie, acknowledged that he and Brief were friends by making the crew sign.

Crew Strength
Brief, as the captain, was likely the strongest person on his crew. Though the rest of the crew's strength wasn't seen, they were easily defeated, captured, and killed by the Red Arrows Pirates.

Trivia

 * The Mustache Pirates had a group sign to acknowledge that they were all friends, which was putting your finger under your nose to make a finger mustache.
 * The crew's identical appearance with their captain is something that rarely happens in the series, only with this crew and Brief and the Caribou Pirates and their captain Coribou.