To do this glitch, you must first execute the Pomeg Berry Glitch, which is done by using a Pomeg Berry on a Pokemon with 1 or 2 HP so that its HP loops to 65,535 (displayed as ?35 in-game). Do so, however, with only one Pokemon and an Egg in the party, with the Egg in the top-leftmost slot of the party in the Pokemon menu. After executing the glitch, you will now be able to enter battles and use the Pokemon Egg as if it were a normal Pokemon. It will function as a normal Pokemon - you can view the stats it will have upon hatching, it can level-up by beating Pokemon, it can learn new moves, it can even evolve. This means that you can alter the Pokemon inside the Egg in otherwise-illegitimate ways. For example. Pikachu cannot normally know Thunder when hatching from an Egg at Level 5; through this glitch, Pikachu can. Similarly, you can hatch Eggs with fully-evolved Pokemon such as Typhlosion, Meganium, and so on, inside.
Meet the conditions below, then speak with the Game Freak director in Celadon City to get the following diplomas.
Note that Mew, Celebi, Jirachi, Deoxys, Shaymin, Darkrai, Manaphy, Phione, and Arceus do not count towards this, and are thus not needed.
For this glitch to work properly, you must have a Pomeg Berry and a Pokemon who has not had their HP lowered as much as possible already through Pomeg Berries. (If the latter is the case, the use of HP Ups on the Pokemon will suffice.) Get the Pokemon to a severely low level of HP (1 or 2 HP). Once you do so, in the field, use the Pomeg Berry on the Pokemon. This will in turn cause the data in their HP to cycle back to the top of the counter, giving the affected Pokemon 65,535 HP - over 90 times the otherwise possible maximum in the game.
By completing certain tasks in the game, you get stars added to your Trainer Card. (Of special note are the Shiny Leaves, found only by speaking with your Pokemon in certain areas on very rare occasions, the locations being Nature-dependent.)