A system to input coordinates, or some location, and command a skeleton army to travel there and attack any enemies (and enemy players) there.
Another system to command skeletons to track and move towards enemy players and kill them.
Finally, a system to cancel such attack orders and have the armies return to the player.

This could perhaps be done by creating an item called an "Attack Plan" or a "War Plan" and having the user input instructions (in the form of coordinates, enemy player name, etc.) into an interface. The plan will be saved in the item (maybe with some codename written by the player, e.g. "Attack Plan: Operation Cupcake").

When activated on a certain army, that army will carry out the orders in the plan. This item could perhaps be crafted using a map and ink sacs or something like that. Also, allow the attack plan to be cancelled at the player's request using the item.