There's two parameters to edit. For the first one, which is required, type how many Pokémon your Pokédex says you have. The second one is optional; you can type what game you're referring to. Leave off the "Pokémon" part of the title.
{{User:The Raven's Apprentice/Userboxes/User PokéDex|75}}
{{User:The Raven's Apprentice/Userboxes/User PokéDex|126|LeafGreen}}