Dual-slot mode, often called the dongle method, is one of the many ways that people can get Pokémon that are outside of the Sinnoh Dex, especially Pokémon that are exclusive to other regions, by using the GBA games of the series as dongles for the DS games. With one of the five Game Boy Advance games inserted into the GBA slot of a Nintendo DS while playing either Diamond or Pearl, you can find Pokémon not otherwise available in Generation IV in certain areas of Sinnoh, but only after you have unlocked the ability to use Pal Park. Using the dual-slot Mode with all five GBA games and trading version-exclusive Pokémon between Diamond and Pearl, you can get all Pokémon excluding Tangela, Tropius, the starters, and legendaries of previous generations.
Ruby in the GBA slot
Pokémon - Location
Seedot - Routes 203, 204 and 210, Eterna Forest
Nuzleaf - Routes 210 and 229
Mawile - Iron Island
Zangoose - Routes 208 and 210
Solrock - Lake Verity, Lake Acuity, Lake Valor, Mt. Coronet, Sendoff Spring, Turnback Cave
Sapphire in the GBA slot
Pokémon - Location
Lotad - Routes 203, 204, 205, and 212 (south)
Lombre - Routes 212 (south) and 229
Sableye - Iron Island
Seviper - Routes 208 and 210
Lunatone - Lake Verity, Lake Acuity, Lake Valor, Mt. Coronet, Sendoff Spring, Turnback Cave
Emerald in the GBA slot
Pokémon - Location
Pineco - Eterna Forest, Routes 203, 204, and 229
Gligar - Stark Mountain, Routes 206, 207, 214, 215, and 227
Shuckle - Route 224
Teddiursa - Route 211, Lake Acuity
Ursaring - Routes 216 and 217, Lake Acuity
FireRed in the GBA slot
Pokémon - Location
Caterpie - Route 204
Metapod - Eterna Forest
Ekans - Route 212 (south)
Arbok - Great Marsh
Growlithe - Routes 201 and 202
Elekid - Routes 204 and 205, Valley Windworks
LeafGreen in the GBA slot
Pokémon - Location
Weedle - Route 204
Kakuna - Eterna Forest
Sandshrew - Wayward Cave
Sandslash - Route 228
Vulpix - Routes 209 and 214
Magby - Route 227, Stark Mountain
Any Generation III game in the GBA slot
Pokémon - Location
Haunter - Old Chateau
Gengar - Old Chateau
Ruby in the GBA slot
Pokémon - Location
Seedot - Routes 203, 204 and 210, Eterna Forest
Nuzleaf - Routes 210 and 229
Mawile - Iron Island
Zangoose - Routes 208 and 210
Solrock - Lake Verity, Lake Acuity, Lake Valor, Mt. Coronet, Sendoff Spring, Turnback Cave
Sapphire in the GBA slot
Pokémon - Location
Lotad - Routes 203, 204, 205, and 212 (south)
Lombre - Routes 212 (south) and 229
Sableye - Iron Island
Seviper - Routes 208 and 210
Lunatone - Lake Verity, Lake Acuity, Lake Valor, Mt. Coronet, Sendoff Spring, Turnback Cave
Emerald in the GBA slot
Pokémon - Location
Pineco - Eterna Forest, Routes 203, 204, and 229
Gligar - Stark Mountain, Routes 206, 207, 214, 215, and 227
Shuckle - Route 224
Teddiursa - Route 211, Lake Acuity
Ursaring - Routes 216 and 217, Lake Acuity
FireRed in the GBA slot
Pokémon - Location
Caterpie - Route 204
Metapod - Eterna Forest
Ekans - Route 212 (south)
Arbok - Great Marsh
Growlithe - Routes 201 and 202
Elekid - Routes 204 and 205, Valley Windworks
LeafGreen in the GBA slot
Pokémon - Location
Weedle - Route 204
Kakuna - Eterna Forest
Sandshrew - Wayward Cave
Sandslash - Route 228
Vulpix - Routes 209 and 214
Magby - Route 227, Stark Mountain
Any Generation III game in the GBA slot
Pokémon - Location
Haunter - Old Chateau
Gengar - Old Chateau
