CheatCodes.com has all the official Yu-Yu Hakusho: Spirit Detective GBA cheats to unlock everything. If you know of any that we don't have, please let us know.
All published and official codes as of Tuesday May 21, 2013 for Yu-Yu Hakusho: Spirit Detective are shown below.
Both Hiei and Kurama need to get to at least lv.15 to learn there 2nd move and around 20 to get there 3rd move.
Battle 1: Shorin/Use shotgun Battle 2: Spirit Beast/Use shotgun Battle 3: Kyukonki/Use spirit gun Battle 4: Baldock/Use shotgun when you see him Battle 5: Demon 1/Use spirit gun and spirit punch Battle 6: Rando/Use shotgun Battle 7: Genbu/Use spirit gun Battle 8: Demon 2/Use shotgun Battle 9: Seiryu/Use shotgun Battle 10: Gokumonki/Use spirit gun Battle 11: Suzaku/Punch him and use shotgun Battle 12: Spider/Use shotgun Battle 13: Demon 3/Use spirit gun Battle 14: Helen/Use shotgun and spirit gun Battle 15: Miyuki/Use shotgun Final Battle: Toguro/Run around and use shotgun(Note: If these hints don't work, beat your enemies the way you did in story mode.) I hope this hint helps you.
Here are the directions on how to beat Suzaku: First, start hitting him until he splits into 7 guys. Use shotgun until he's 1 guy again. When you have low health and energy, go to the bottom left and right of the area. You will find power-ups. Repeat. Power-ups will regenerate every few minutes.
To beat Hiei, face the top platform and dodge his blasts. When he comes out, hit him with spirit gun. (Note: If you get hit by his blasts, you won't be able to move for a couple seconds and he will get on your platform and hit you. However, when you can move again you can hit Hiei with spirit punch.
To get the shotgun (Yusuke's best attack), you need to beat Rando. Then you will fight Gen Kai. She has all of Yusuke's moves(including the shotgun), and is slow. After that you'll get the shotgun and go off to fight the Saint Beasts.
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