X-Kryptonite
From superman.nu: Supermanica
X-Kryptonite
An artificial isotope of Kryptonite that is accidentally created by Supergirl in a failed attempt to create an antidote to Kryptonite exposure, X-Kryptonite is able to temporarily give Streaky the Supercat powers beyond those of mere mortal cats, equal to those possessed by the Girl of Steel (Act No. 261, Feb 1960: "Supergirl's Super-Pet"; and others). It is later revealed that X-Kryptonite can weaken super-powered Kryptonians as well (SF No. 203/1, Sep/Oct 1980: "The Supergirl from Planet Earth").
