This could be nice to place zombies in a container
And let player open the container and free them to block some path
For the opponent or increase the difficulty to kill you.

Also put less zombies in other areas and place them
In strategic locations.

So the zombie population could be changed by players
And adding some strategic interactions in the battle.

This feature should be easy to implement , i mean placing
Spawners in containers like in resident evil film when they search fuel
In las Vegas.
(Red container with viral and blue ones with biters
Or whatever monsters)


The only problem is to make openable doors for containers
But the roller shutter doors could do the trick.

Also the other point is to inform players that they can
Use it for the battle.
Some zombie icon or biohazard icon on containers
Plus a marker on the hud or a quest description
Or hint to inform player.

As your design is already in place, maybe you can use
Existing assets instead of new containers?

It ´s just an idea but it could be fun.

@cr1m3 - That is quite an interesting idea. I think I'll take a look at that.