A Dummy unit is any unit with the
Locust ability - which makes a unit unselectable, uncommandable (outside of triggers), untargetable, invulnerable, and prevents it from being influenced by "nearby unit" effects (auras, aoe abilities, set unit group, etc).
View attachment 481404
People use these to cast spells on command. For example, a Dummy unit could cast Bloodlust on a group of allied units. You've probably played a custom map before where a common spell that normally targets 1 unit was able to target a group of units instead (this is how).
A standard Dummy setup:
1) Copy and paste the
Locust.
2) Set
Model = None,
Shadow = None,
Attacks Enabled = None,
Movement Type = None,
Speed Base = 0.
3) Optionally, you can download and use this
Dummy model as well as modify the unit's
Art fields to make missiles/special effects appear correctly.
A Dummy "attacker" simply implies that the Dummy unit has it's
Attacks Enabled = Attack 1 Only, and it's role will be to attack enemy units rather than to cast spells.
So using triggers, you would create these Dummy unit(s) on top of your Guard Tower (they have no collision and are completely hidden from sight) and use them to handle the extra attacks. You're creating the illusion that the Guard Tower is attacking multiple units when it's really the Guard Tower + multiple "Dummy guard towers" stacked on top of it. It's not the easiest thing to setup though, because these units can and will try to attack the same target, so you'd need a system in place to prevent that.
Maybe Cheshire knows of an existing system or can create one for you.