Go to The Orchre Picnic game and go to the section on the very right. You will find a cave. Say "cave" to Pikachu and he will come out with a Togepi Egg. Abra will fall out of the sky.He will take the egg. Visit the shop often enough to hatch the egg. If Pikachu had bought a balloon the time Togepi hatches, he will give the baloon to Togepi!

Beat the Pinata stage with Venusaur perfectly and you shall be taken to a hidden stage. The stage is an overnight campout with Pikachu. Haunter shall sneak up on Pikachu and scare him occasionally.