The Flash: 10 Best Characters Who Only Appeared In One Episode
3. Plastique
One of the more tragic characters on this list, Bette Sans Souci was one of the first metahumans that Team Flash encountered that was not antagonistic, but was instead in need of urgent aid.
Once a sergeant in the US military, she was retired from active service due to an injury she sustained following an explosion in Afghanistan. She gained her incendiary abilities when her operation room was bombarded by dark matter from the particle matter explosion.
Her newfound power made her a force to be reckoned with, but also put a target on her back as she quickly endured torture (under the guise of experiments) from her supposed benefactor, General Wade Eiling. Later on, she crossed paths with Team Flash, who attempted to help cure or at least control her metahuman abilities.
Unfortunately, S.T.A.R. Labs does not have the technology to control her abilities and she opted to kill Eiling (after some convincing from Harrison Wells). Sadly, her plan failed and she was shot, turning her into an incredibly powerful explosive that was quickly stopped by Flash in the nick of time.