When Shellder bites Slowpoke's tail, it is now bipedal. Its feet are more muscular, and its belly has scales to protect it, compared to Slowpoke.
Slowbro can have the ability Oblivious or the ability Own Tempo. Oblivious prevents Slowbro from getting infatuated. Own Tempo prevents Slowbro from getting confused. Slowpoke can evolve into a Slowbro if a Shellder bites on its tail. This triggers Slowpoke's evolution, and allows for the Slowpoke to stand on its hind legs (the Shellder acts as a counterbalance). It may be possible that if the Shellder was knocked off of Slowbro's tail, it would turn back into a Slowpoke. It has various moves such as Calm Mind, Slack Off, Surf, Ice Beam, Psychic, Flamethrower, and Grass Knot.
Slowbro evolves from Slowpoke starting at level 37. It will evolve into Slowking when trading it while holding the King's Rock. It can also further evolve into Mega Slowbro using its Mega Stone. Slowbro gets this Mega Evolution in Omega Ruby and Alpha Sapphire. In the anime Slowpoke evolves into Slowbro when a Shellder bites its tail and Slowking is an alternate evolution that happens when a Shellder clamps its head while wearing a King's Rock.