Yesterday, we learned that Pom Klementieff was cast in James Gunn's Guardians of the Galaxy Vol. 2. There were no details on the character given at the time, but now thanks to Deadline, we do know who she'll be playing. According to the report, she will be taking on the role of Mantis.

Mantis was created by Steve Englehart and Don Heck, and she first appeared in Avengers #112 in 1973. Mantis is the half-Vietnamese, half-German daughter of the antihero Libra, and a martial arts expert with psychic abilities and ties to the alien Kree race. She also has a connection to the Avengers and Thanos in the comics. I'm not sure if those connections will be utilized in the MCU, but there's obviously a possibility. As far as her powers and abilities go, here's some information from Marvel: