If you have a transfer pak, then this is a great cheat. Put in any pokemon game and follow instructions below.

If you have a Girafarig, go to mini-games. Play Furret's Frolic. You can play as your Girafarig.

If you have an Omanyte, it can replace Togepi in Tumbling Togepi.

If you have Pokemon Yellow, You can be you Pikachu in Pichu's Powerplant.

Hint: Don't evolve the pokemon! You cant use it in your mini-games! There may be more, but you'll have to find them out! Good luck!