Several highly sought-after Pokémon have low encounter rates or require specific conditions to find.
Located at the top of the Tin Tower in Ecruteak City. You need the Rainbow Wing to encounter it. The Kanto Birds Articuno: Found in the Seafoam Islands. Zapdos: Located at the Power Plant outside Cerulean City. Moltres: Hidden deep inside Mt. Silver. Generation III Additions pokemon liquid crystal pokedex
All three can be found and captured through gameplay. pokemon liquid crystal pokedex