Saibra

 was a mutant human who would replicate a person when touching any form of their organic matter.

As she was unable to control this ability, she helped the Twelfth Doctor rob the Bank of Kalabraxos, in order to gain a gene suppressant. During the mission, she briefly impersonated Clara Oswald (to demonstrate her power) and impersonated a businessman named Porrima to facilitate entering the bank. (TV: Time Heist)