Transmutation (animal) – The ability to turn humans into animals.
Circe had the ability to turn humans into animals. Generally turning a superhero into an animal is a one-shot affair but the exception in the DC universe is Comet. Circe (DC) is one of the few Silver Age characters that does both bad deeds and good deeds in different issues of Action Comics. Lex Luthor occasionally shows remorse in the Silver Age but does not out and out do good deeds. Generally Silver Age characters are always good or always bad unless they are victims of mind control which is not the case with Circe (Action Comics V1 #311).
Lockjaw (Marvel) speaks in The Thing V1 #3 and therefore is a human that has been transformed into an animal by the Terrigen Mist of the Inhumans. Lockjaw always acted like a dog before he spoke and after he spoke and one has to wonder why he did this given his fellow Inhumans would have to know he was an intelligent being that could talk! This issue is explained away as a joke by Karnak and Gorgon. However, what if the joke is in fact the lie and the Inhumans have their own form of racism that condemns those transmuted into animals into a none human abyss!
Lois Lane is another Silver Age character that was constantly being turned into an animal or animal hybrid (Jimmy Olsen V1 #66, Lois Lane V1 #11, Lois Lane V1 #92, Lois Lane V1 #12).
There was plenty of one-time animal transmutation in the Silver (Action Comics V1 #284, House of Mystery V1 #145, Wonder Woman V1 #170).
Superboy was turned into an animal or animal hybrid several times in the Silver Age (Superboy V1 #178, Superboy V1 #142, Superboy V1 #194, Superboy V1 #103).
The Silver Age Superman has been turned into animals or animal hybrids several times (Lois Lane V1 #70, Superman V1 #165, Action Comics V1 #303, Action Comics V1 #296, Action Comics V1 #243, Superman V1 #139).
Vixen (Marvel UK) was a supervillain but was turned into a fox in Mighty World of Marvel V2 #8.