助紂為虐

lit. helping tyrant Zhou 商紂王|商纣王[Shang1 Zhou4 wang2] in his oppression (idiom) / fig. to take the side of the evildoer / giving succor to the enemy

to help / to assist

(bound form) Zhou, pejorative name given posthumously to the last king of the Shang dynasty 商紂王|商纣王[Shang1 Zhou4 wang2] (the name refers to a crupper 紂|纣[zhou4], the piece of horse tack most likely to be soiled by the horse)

crupper (harness strap running over a horse's hindquarters and under its tail)

as (in the capacity of) / to take sth as / to act as / to serve as / to behave as / to become / to be / to do / by (in the passive voice)

because of / for / to

oppressive / tyrannical