Baseball hat Mankey
In the river canyon area, there are 4 Mankeys throughout. The first Mankey is just before the fist set of Geodudes. The second Mankey is on the left side of the river just after you see the first Golem. You will see the third Mankey on your right just before you go down the steep hill. The last Mankey is on the right(it's the one you have to hit with the squirtle to get to the next area). You must use the pester ball to knock down the first three Mankeys then use the squirtle to knock down the last Mankey. When you get to the button that opens the gate to the next area, you will see a Mankey with a baseball hat on.
Hitting the Mankeys with the pester ball is very hard to do and I was only able to get the Mankey with the hat one time. So good luck and happy shooting.
Added by: urialmckenney Sep 27th 2012, ID#6629