When you leave the gym, you will get a call from Professor Utsugi. He is telling you to go get an egg at the pokemon center. So do so. You will see a man with glasses at the pokemon center. Leave a space in your 6 slots for it. After, go to a path on the west side of town and south until you see several caves. There is a woman in one of them. This is where to solve the Kabuto Puzzle. It is not very difficult. Solving this puzzle will awaken some of the pokemon. Then you will be dropped down to another cave. You will see Magnets of all different shapes. They are the same Pokemon. So catch one.

Go back on the path heading east until you see another path. Go south and fight all the trainers. There is a pokemon called An'Noon. Catch it if you like. When you get to a person who asks you for 100 yen, say yes. Then go to the Pokemon Center. There is a fisherman there who will give you a rod. Use the rod to catch a magikarp.