[Eru]

The way I was thinking would depend on players protecting the tower. Giving people the ability to plant protective units would be more difficult.

The thing that springs to mind would be to have the attacking guys drop a currency that can be used at the tower to buy defense units that are basically items that are added in that look like little mages, etc (shrunken mobile item IDs). Then another spawner could search for those, then if it finds one laying around somewhere, it would delete it and add the appropriate unit in its place.

To get it to attack the attacking units, you could use the 'team' functionality that's built into the mobile class. Mobs of different teams will attack each other, so just set the defending units to team1 and the spawning monsters should be team0 by default. Not sure, really.

I don't have the time to make it myself, but I do like throwing the ideas out there. Here's the reference sheets I always used when poking at spawners if anyone's interested in trying:

https://www.dropbox.com/sh/rd5omkah661hj...er2doc.txt
https://www.dropbox.com/sh/rd5omkah661hj...awner2.txt