Zoo Keeper - Platform: Nintendo DS

Expert difficulty:
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Record the top score in Zoo Keeper, Tokoton 100, Quest and Time Attack modes. 

Gekimuzu Difficulty:
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To obtain a 4th difficulty, you need to get the highscore on all 4 modes of gameplay.
Zoo keeper  - 1200000+ points needed.
Tokoton 100 - 1800000+ points needed.
Quest mode  - 10000+ Yen needed.
Time attack - 600000+ points needed.

After getting all 4 high scores, a 4th difficulty appears in the top line of the option menu.
This difficulty means "Expert" or literally "difficult-player" and has a huge advantage of 
doubling all the normal points you achieve. 

Expert difficulty:
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Record the top score in Zoo Keeper, Tokoton 100, Quest and Time Attack modes.