im my map, when someone uses a certain spell, a barrage of scourges AKA "missiles" flies to a target and each scourge is suppose to do a little damage to a ground unit AKA the target. How do you make the scourges do damage to a ground unit? I know there is a modify unit hp trigger, but that dosent work for me because like.. is it is set to put the target at 80% hp, then the first scourge would do that, then the rest of the sourges would just die with pretty much no effect, and also, if the target is less than 80% hp, it would basicly heal it. Are there any other ways to trigger scourges to do damage to ground units through triggers?

Simply put, no. The only way its possible is through some form of virtual hit points, where you use death counters to keep track of the actual health, and modify the death count to subtract "health". Then the scourage basically is just a visual effect. Set up a death count for the units HP, then at certain amounts use the Modify Unit HP to certain percents so the unit looks just like the scourage is damaging it, but in reality you're just detecting the scourage in the vicinity of the unit and subtracting from the death count.

actually, that idea will work for what im doing. thanks ;D you can lock this now

Alternatively you can cycle through the scourges using Give Unit and use a Direct Damage System.

actually i had a new easier idea of having 2 different spells, 1 for air and 1 for ground. The anti air spell spawns scourges, the anti ground spell spawns a barrage of scarabs (yes i know how to trigger that ;D) this way i can easily set up the amount of damage i want done. I was going to use infested terrans because its a lot easier to trigger, but the splash could kill the hero. Also scarabs look better.

DDS. Check this out, as yoonkwun said.