Hi guys. Help me sort out the best way to do this.
There are 2 computer players (spawn units)
and two teams of humans (3v3 1 hero each player)

A spell I have effects nearly half the screen, it is supposed to be a swarm of locusts.
I am using a dds for the damage of the spell. So far I have an idea for how to apply the dds in the locust area to the human heroes, but how can I make it so that it will also damage the (multiple) spawn units that might be under the area? Best to just leave spawn unaffected?

You can try using both computers as scarab owners (and targets in DDS for each other). This will mean that you'll be running the AI for all their units, though. Try it out and see what happens, because I don't know.

One of the big problems with starcraft, is that there is no real efficient way to "mark" units. If we had an action "Mark Unit X with Flag Y" and a way to detect it, something like you propose affecting half the map would be much more feasible. As starcraft stands now however, you'd probably have to pull some nonsense like giving all the units to be affected to a different computer player, deal damage to 1 individual unit, then give it back and re-order it to whatever it was already doing, then continue to the next individual and deal damage, give it back, re-order it, ect. Depending on the number of units in your location, the amount of damage you need to deal, and the number of scarabs you have stored, you could run out of scarabs long before all the damage is dealt, I imagine. Doesn't seem very feasible to me, but *shrug* best of luck.

Yeah that was the (bad) solution that I had thought of. Might just keep it from effecting spawn.

As a part of the Spell Generator that I'm currently working on, I'm dealing with Area of Effect Spells, and one of the effects Included is Damage.

I used a Mobile Grid to detect Areas at which the scarabs would spawn, and then did several Direct Damage Systems that were routed off of that.

If you follow my path, you will (most likely, depending upon how much dmg you're wanting here) run out of scarabs, or run into CCMU. What I did to avoid this was to increase the scarab damage by some factor, and then have less scarabs deal the same amount of damage. I don't know if this solution works for you or not, but it works for me.

Yeah the major limiting factor of dds scarab use is 1) how frequently spells are cast and 2) how flexible you need the damage to be. I would be using a low number of scarabs no more than twice per second per player (6) so it should be fine. Also most spells currently do not need to use the dds for their damage although a few do. Curious about your spell generator though.

If you have 4 computer players useable, you can have the scarabs do different amounts of damage each (1, 2, 4, 8). This would allow you to deal damage faster with less scarabs total.

There are 2 cpus available.

So have one do 10 dmg, and the other one do 1 dmg. That way, you can easily calculate and use litte amounts of scarabs.

Yeah I know but that's not the problem xD