Today, there is kryptonite, which can kill
Superman in minutes and anyone else with prolonged exposure.
Yesterday, there was Green Kryptonite (kills any Kryptonian in minutes) ; Red Kryptonite (temporarily alters any Kryptonian, e.g. renders ant-headed, giant-sized, or evil) ; Blue Kryptonite (only affects Bizarros) ; White Kryptonite (kills all plantlife) ; Jewel Kryptonite (gives mind control to Phantom Zone residents) ; X-Kryptonite (gives Streaky the Supercat his superpowers).