Bonsly

From the Pokémon Encyclopedia

Bonsly is a 4th generation pokemon that is the pre-evolved form of Sudowoodo. It is also a Rock type. So far, the only known way to obtain one in the generation IV games is to catch the single sudowoodo in Pokemon Emerald, at the Battle frontier, then use pal park to transfer it to Pokemon Daimond, Pearl, or Platinum, and then breed it with a Ditto. Brock also had a Bonsly, and eventually evolved it into a Sudowoodo.