In-Game Reset
Hold A + B + Select + Start while playing the game to reset.
All Three Starter Pokemon
To get all three starter pokemon, you will need either Pokemon Silver or Pokemon Gold. First, begin a new game on Gold or Silver. Then, choose any starter (Cyndaquil, Tododile or Chikorita). Go to the first Pokemon Center that you can find, then trade one of the starter Pokemon for another. You can repeat this as many times as desired.
Quick Restore
When far away from a Pokemon Center, go to a location with a PC. Deposit the weak Pokemon, then withdraw it.
Increasing Pokemon Happiness
Buy thirty each of Carbos, Protein, Iron and Calcium. Give as many of the Carbos, Protein, Iron and Calcium to your Pokemon as possible. Next, take your Pokemon to the groomers and have it groomed twice. Then, take it to the Happiness rater to see how much it likes you. After that, raise it up a level and it should evolve. This is best used with Togepi to Togetic, Eevee to Espeon, Eevee to Umbreon, and Chansey to Blissey.
Evolve by Trading
Machoke, Kadabra, Haunter and Graveler will evolve by trading via a game link cable.
Go to: Pokemon Crystal Info Page | nGaming Home Page.