When you start the scene with Genesis and Hollander in the Hills of Gongaga fight up to seven battles and then leave the area. When Zack notices a chest falling down the waterfall select the 'I bet there will be more' option and play the treasure chest mini-game. Monsters will come down as well as chests. The boxes and monsters come down four times repeating the same pattern.
Wave 1 (chest): Middle
Wave 2 (monsters): Left and Right
Wave 3 (chest): Far Left
Wave 4 (chest): Far Right
These waves will repeat four times after the fourth wave. The more boxes you get the better the prize. The best way to dodge them is to get out of the river then go back in once they are gone as Zack becomes temporarily paralyzed if you touch the monsters.
Added by: Sanzano Feb 16th 2011, ID#3885