Here is my design for a wall mounted zombie dispenser.
When the player steps on the pressure plate, the sticky piston retracts and the dispenser will then spawn a zombie into the wall with its head occuping the space where the retracted block was, so that it doesn't suffocate. (NOTE: there is a delayer leading to the dispenser in case you can't see that.)
when the player then steps of the pressure plate, the zombie, if it is still in the wall, will be pushed out into the corridor.
A better redstone technician than I could make the piston push the zombie out right away, rather than when the player steps off the plate. but this was just a quick prototype anyway :smile.gif: