1 credit = 1 Pokemon/Service. Also, here are some tips, if you're RNGing, I suggest you use Pikatimer, it will be much easier for you to RNG if you will use that. It's in the first page of the RNG question thread, just download it and follow the instructions; Also, if you're RNGing for Wondercards, I suggest you RNG it from your HeartGold and get the Pokemon from the Cerulean or Fuchsia City Pokemart since there are no wandering NPCs there which will ruin your frame. :)