Kyle Nimbus

Kyle Nimbus or also by his nickname The Mist, they was the main antagonist of the episode Things You Can't Outrun, of season one of The Flash.

Background
Kyle Nimbus worked as a hit man for a mafia family that was the Darbinyans, until Kyle was arrested by detective Joe West, he was soon betrayed by the Darbinyans and sentenced to death by judge Theresa Howard. However, one night when Kyle was scheduled to run, the particle accelerator explosion of Laboratories S.T.A.R.S. soon hit the gas chamber where Nimbus was merging his molecular extrusion with the toxic gas, days later, Nimbus was pronounced dead, and he soon escaped from the Iron Heights Prison necrotereum, and began his plan of revenge on those who caused it your death.

Things You Can't Outrun
Kyle soon afterwards took revenge on the Darbinyan family, he then entered a meeting disguised as an employee of Amarasia Oasis, he then poisoned all members of the Darbinyan family for his participation in his execution, killing them shortly afterwards. After killing the Darbinyan family, he soon went to his next target, judge Theresa Howard, who sentenced him to death, and was responsible for his death. He killed her when Howard was in the mall elevator, suffoncing her to death with her venomous gas and simply killing her. Soon his last target was Joe West after a fight he had against Flash, he first defeats Flash without receiving any damage because his body is only gas due to mutation, however, Flash soon used it and managed to defeat the Nimbus and put him in the prison packed with metahumans.

Time in the Pipeline
Kyle tried to kill Cisco when tried to feed him, causing Caithlyn Snow to suck him by vacuum cleaner, so Cisco tried one of Brie Larvan's bee stealing to feed him more. Kyle destroyed them.

Escape from the Metahumans Prison
Soon after Kyle and the other Metahumans were being transferred from his prison. They soon managed to get a favor from Leonard Snart. However, they soon began quarrel between them specifically, Kyle, Mark Mardon and Jake Simmons, soon after Kyle tried to kill Flash, which he then vibrated fast that created winds that disabled Kyle, Mardon hit Flash and knocked him to the ground, Kyle so took the opportunity to escape.

Powers
It can turn your body into poisonous cloud gas of cyanide mixed with sedative, and it can through certain things due to your body being smoke toxic.

Trivia

 * The actor who plays Kyle Nimbus, who is Anthony Carrigan, also plays Victor Zsasz of the Gotham franchise.