Here are some cheats for Pokemon Diamond:
Unlockable: Elekid
Insert Fire Red in the GBA slot.
GBA Cartridge Extras
Unverified
. Insert the GBA cartridges to find the following Pokemon (you still need to find and capture them yourself).
Ruby
Seedot
— Hakutai Forest, Route 203, Route 204
Nuzleaf
— Route 229
Mawile
— Iron Island
Zangoose
— Route 208
Solrock
— Thrust Lake, Thrust Lake Surroundings, Wisdom Lake, Aspiration Lake, Tengan Mountain, Departure Springs, Return Cave
Sapphire
Lotad
— Route 203, 204, 205 North, 212 South
Lombre
— Route 212 South, 229
Sableye
— Iron Island
Seviper
— Route 208
Lunatone
— Thrust Lake, Thrust Lake Surroundings, Wisdom Lake, Aspiration Lake, Tengan Mountain, Departure Springs, Return Cave
Emerald
Pineco
— Hakutai Forest, Route 203, 204, 229
Gligar
— Hard Mountain, Route 206, 207, 214, 215, 227
Shuckle
— Route 224
Teddiursa
— Route 211, Wisdom Lake
Ursaring
— Wisdom Lake, Route 216, 217
FireRed
Caterpie
— Route 204 South
Metapod
— Hakutai Forest
Ekans
— Route 212 South
Arbok
— Safari Zone
Growlithe
— Route 201, 202
Elekid
— Route 204 South, Powerplant
LeafGreen
Weedle
— Route 204 South
Kakuna
— Hakutai Forest
Sandshrew
— Lost Cave
Sandslash
— Route 228
Vulpix
— Route 209
Magby
— Hard Mountain, Route 227
Any Pokemon GBA Cartridge
Haunter
— Forest Mansion
Gengar
— Forest Mansion Room with eyes
Unlockable: National Dex
Finish the Shinou Dex.
Unlockable: Pal Park
Acquire the national dex.
Find more Nintendo DS Walkthrough – Cheats For Pokemon Diamond at http://www.videogameshintsandcheats.com/ActionReplay-Codes
Great prices on NDS Lite accessories at http://www.videogameshintsandcheats.com/Accessories/Nintendo-DS-Lite