He can catch you by surprise doing this, so try to keep an eye on him at all times.
Aim a little higher than the target to cover the distance and height of the targets.
This makes him vulnerable to the Fazer Blaster and Faz Camera.
If Gregory goes to Monty's Gator Golf, he will find a Mazercise ticket and logs mentioning that Monty has been damaged previously by the Splash Bucket up on the catwalks.
In the "True Ending", Monty is down in the buried pizzeria along with Glamrock Chica and Roxanne where he tries to make it into the office to attack Gregory.
You will see his dismembered arms lying there.