Given seed is seed[x] when you encounter Cresselia, Cresselia is created from seed[x+5], seed[x+6], seed[x+7] and seed[x+8].
If you calculate seed of Cresselia you want, and sets up that seed, you can get Cresselia you want.
Seed when start game is created follow means.
(((month)×(day)+(minute)+(second)) mod 0x100)×0x1000000 + (time)×0x10000 + (year)-2000+X
X increases in proportion to the time from starting game until selecting "CONTINUE". In picture of selecting "CONTINUE", speed of increase of X is about 60 per second, and X increases in units of 2.
Year, month, day, time, minute and second is used the time when you select "CONTINUE".
Every time you walk 128 steps in front of Cresselia, seed is consumed the number of Pokemons you have.
