The extract in @Gamer Magazine mentioning the rejected sheep Pokémon
This unnamed sheep Pokémon was a concept for a Pokémon which was inspired by Dolly, the first cloned sheep. It was briefly mentioned in Issue 6 (January/February 2011) of the @Gamer Magazine, where Andy of @Gamer interviewed Junichi Masuda and Ken Sugimori of Game Freak. The Pokémon was rejected because Game Freak decided it would be too controversial.
There is no known artwork for this unreleased Pokémon. It may have been simply a consideration rather than a prototype Pokémon. It's also possible that this concept was later reworked into Mareep. Its type is also unknown.