Stantler because Roselia, Chansey, and Porygon each got 2 more evolutions, whether they be pre-evos or post-evo's
and they started as non evolution pokemon
@oyeah1998 To be more specific, each of these got another stage in the generation after their first appearance, and each of these got another stage in the fourth generation. Exception, of course, is Stantler.
Also, Stantler has only one Pokedex entry between Diamond/Pearl/Platinum.