Evolution Serum
From superman.nu: Supermanica
Evolution serum
Discovered by Circe, evolution serum is an "artificial liquid kryptonite" solution, that transforms a Kryptonian into "the creature [they] most resemble by nature". It contains a small dose of kryptonite, enough to change the drinker biologically without weakening his super-muscles.
Circe pours some of this serum into a cup she offered Superman, making him transform (partially) into a Lion. (Act No. 243, Aug. 1958: "The Lady and the Lion")
