Gaangus are monkey-like creatures capable of climbing on ceilings and ambushing the player. Similar to Skortch, they only attack using melee, and are capable of doing a significant amount of damage in a very short period of time.
Gather all into a group and back away whilst shooting at them from a distance picking them off one by one.
This mob is said to be the mascot of Code Avarice and will appear in all of their games in some fashion (Source: Developer Travis Pfenning)
They are most commenly refered to as "ceiling monkeys" due to the fact that the can jump on the ceiling, and are monkeys.
These enemies can sometimes attack through thin structures such as walk ways.