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Tricks with Negative IDs

I found a lot of people - including very capable scenario designers, far better than me, don't know how to use the Negative Unit Id Tricks!
You have two heroes - each with an ability activated while pressing the unit garrisoned inside it. Try and figure out how the triggers work!

Normally, every unit has an ID - a number from one up. When you use an external program to change a unit's id to a negative number, all sorts of weird things happen - and when you have two units with the same negative ID, you can do even more weird stuff.

I found these mostly by trial and experimentation, though there are some handy resources at http://aok.heavengames.com/university/design/the-double-negative-effect-units-with-negative-ids/ to get you started.
To see how these are done, you will probably need the external editing program Trigger Studio - AOKTS.