Instructions
Click on the "Start" button on your Nintendo DS console and select the "Pokemon" option. Highlight the Poliwag from the roster list and press the "Select" button. Scroll up and highlight the first Pokemon in your roster list and press the "Select" button again to place Poliwag as the primary Pokemon in your party.
Search for wild Pokemon in the tall grass, trainers or gym leaders to battle. Winning battles against trainers and wild Pokemon with your Poliwag will increase its experience points and cause it to level up. If your Poliwag is not strong enough to battle trainers or the wild Pokemon in the area, send out a strong Pokemon immediately after Poliwag is summoned into battle. Poliwag will still receive experience points for going into battle.
Continue leveling up your Poliwag until he reaches Level 25. In "Pokemon Crystal," Poliwag evolves into Poliwhirl at that level. Your Poliwag will begin the evolution process immediately after battle,