Awesome game, I can hardly stop playing it. But it has some hard monkey acheivements. Like this one.

Torque Bow - y
Torque Bow - b
Longshot - y
Longshot - b
Boltok Pistol - y
Shotgun - b
Neck Snap -a to pick them up, then x
Curb Stomp -x (any gun)
1 2 3 Punch - y (gun not on this list)
Boomshield - y
Lancer - b
that's hard to know.