Note: Just in case your confused, Mawmen was the other word used to describe the Headcrabbed zombies.
I know that Mawmen are slow and are not supposed to be bright, but they’re not completely stupid either. In the chapter, We Got Hostiles, they were smart enough to sneak through the vents and grab one of the Barnies. In the demo, Uplink, it’s suggested that they were working with the Houndeyes to lure you towards them and to trigger a trap which boxed you in with them.
What if you enhanced the Mawmen’s abilities, such as the ability to pick up wrenches and throwing them at you, the ability to climb a ladder and a rope, and the ability to crouch and climb through vents. Also, why not give them the ability to work with other Xen creatures to improve their efforts in trying to defeat you? They would still be slow and easy to kill, but I think some basic intelligence could be beneficial to the gameplay.