PokémonMega SlowkingIf you haven't been keeping up with Pokémon, I'll give a brief recap of what's been added to Slowpoke and Slowbro since the beginning.
Slowpoke can now evolve into Slowking instead of Slowbro. The transformed spiral Shellder attaches to its head instead of its tail and makes it intelligent.
As of Generation 6, Slowbro can now Mega Evolve into Mega Slowbro in battle through the use of a Mega Stone called Slowbronite, raising its Defense to an absurd degree. Mega Slowbro looks like this.
Slowbronite can't be used with Slowpoke or Slowking. Slowking cannot Mega Evolve.
However, I don't believe there is a biological difference between the three pink things involved in the Slowpoke family. Many Pokédex entries for Slowbro and Slowking talk about how if the Shellder is lost, the pink thing becomes a Slowpoke again. It even loses its enhanced intelligence if this happens to a Slowking. There is even an instance of a Pokédex unambiguously calling the pink thing Slowpoke and the shell Shellder without the context of the Shellder being lost: Mega Slowbro's Pokédex entry in Moon.
When bathed in the energy of Mega Evolution, Shellder converts into impregnable armor. There is virtually no change in Slowpoke.
The names Slowbro and Slowking therefore refer to the union of Slowpoke and Shellder in these particular ways, not enhanced forms of Slowpoke as would be seen if it evolved like a normal Pokémon. The Mega Stone called Slowbronite is actually compatible with the transformed Shellder instead. And you COULD use it with Slowking.
but don't, please