LogFAQs > #967869167

Feebas -> Milotic is similar, as they are both consciously modeled off of Magikarp and Gyarados respectively. Feebas is an ugly fish, Milotic is a thin, mermaid-esque serpent with an iridescent tail fin: stat-wise, essentially a specially-based Gyarados.

Two others come to mind: Karrablast ->Escavalier and Shelmet ->Accelgor, since their stat spreads go in wildly different directions (this is because, to evolve, sneaky, somewhat quick Karrablast steals Shelmet's armor, becoming the slow yet tanky Escavalier, whilst tanky Shelmet, sans armor, becomes the frail yet blindingly fast Accelgor.)