Instructions
Level up Slowpoke through the use of rare candy or through battles against wild Pokemon and trainers. If Slowpoke is too weak to fight an opponent alone, switch it out for a stronger Pokemon when the battle begins. Slowpoke, as well as the other Pokemon, will gain experience points for participating in the battle. When Slowpoke reaches level 37, it will evolve into Slowbro.
Visit the Slowpoke Well in the Johto Region to acquire the "King's Rock." Attach it to Slowbro as a Held Item.
Enlist a friend's assistance. Save your game and turn off your system. Connect your Game Boy Advance system and a friend's Game Boy Advance system using Game Boy Advance link cables. Turn on both systems and load your saved games.
Visit the Cable Club representative of any Pokemon Center to initiate trading. Trade Slowbro to your friend. Slowbro will evolve into Slowking while in your friend's possession. Repeat this step again to acquire Slowking from your friend.