target block for testing weapons
Small grid and large grid block that when placed on a grid, it is in the off position. When the block is switched to on, it turns the entire grid it is attached to, into an enemy grid.
This is basically communicating to your weapon systems, this grid is now a valid target. Destroy it if you see it. As long as the block is powered and on, the grid remains a valid target.
This enables you to make a target for testing out weapon systems. It would be even better if you retained full control of this 'enemy' grid, so you could a) turn the block off and reset it back to a friendly grid, and b) control the 'enemy' grid to make mobile targets.
Yes all of this can be done in Creative, but this is something that would enable server denizens to test their systems without needing a valid enemy in the area.