>>38261481In general most Pokemon retain their core design throughout their evolutions, there are exceptions, mostly Bug-Type Pokemon. In general what you see with most Pokemon is that key components of their design are altered as they evolve, in Bulbasaur's case it's the blooming of the flower, in Charmander's case it's its head shape and the development of wings in the final form. Squirtle is kind of the exception since Wartortle's design is rather different from both Squirtle's and Blastoise's, the cannons on Blastoise follow the same logic as the wings on Charizard mind you.
Some Pokemon designs opt for more change than the Kanto Starters mind you, the Pichu line's ear shape changes in each evolution, as does their tail and Raichu has a pretty distinct colour change from its pre-evolutions.
Honestly off the top of my head the Gen 1 Pokemon that probably come closest to the "It just gets bigger" trope would be Pidgeotto -> Pidgeot, Growlithe -> Arcanine, Poliwhirl -> Poliwrath, Seel -> Dewgong, Grimer -> Muk & Cubone -> Marowak outside of that (and even then I think I'm being a but too restrictive for Seel & Dewgong) the rest seem to change at least one or two aspects of their design, some more and some like Shellder -> Cloyster go through a heavy overhaul to the design. This is true for every generation and cross-generational evolutions seem to be more prone to drastic design changes than intragenerational evolutionary lines.
Pt.1
