A King's Rock is an item introduced in Generation II that allows Poliwhirl to evolve into Politoed and causes Slowpoke to evolve into Slowking when traded. This item also raises chance of causing opponents to flinch by 11.7% with most attacks without any secondary effects.
Omega Ruby and Alpha Sapphire: It can be found in Mossdeep City.
Pokémon Crystal, Gold and Silver Version: It can be found in Slowpoke Well
A King's Rock depicted in the anime