Plasmix was once a Toa of Plasma. He and his team decided to side with Makuta Teridax because they thought it was hopeless to fight someone who conquered the universe. Plasmix was "upgraded" by "Toa" Teridax.Plasmix wears a mask but cannot access the Kanohi Power. He has limited control over Plasma and is stronger than his old body.
Plasmix was based on the Jabberwock S3 of Resident Evil: The Darkside Chronicles. The Jabberwock S3 was B.O.W that was injected with the T-Veronica Virus. The Jabberwock S3 has multiple arms and surprisingly has intelligence so it can understand commands.