Aura Problems. Event?

My friend asked me this...

He wants to make an aura that will add % bonus damage with every unit in range of the aura. So example, 1 unit, 2% damage. 2 unit 4% damage and so on. However The only way to do such aura is by triggers.

And the problem is that I can't find a Event to do this.
The Unit within range event would require an existing unit to be placed, and no variable could be used.

There are a few solutions although, either by creating the unit in advance, or using a periodic timer.

However if there are many units using the same aura, then it wouldn't be feasible to use it.

And using a periodic timer would affect the game in terms of speed and memory.

Are there any ways to solving this problem?
And also what events could be used for Auras?

Thanks in advance.

Why?

Even blizzard auras have a 1 second update interval, so you will be fine with a one second timer, memory depends on how badly you implement it.

Right now, I think that a timer + groupenum combo is the best way for auras, of course, you could do something crazy like range events with things attached to the trigger but it is proven that's slower and messier, so...

You can always play around with Trigger - Add New Event (which will allow you to use variables with Gets Within Range)

You'll need a periodic event (it really isn't that pricey) and a unit
group loop. You'll also need a dummy unit and a dummy ability based off of Inner Fire with each level of the spell corresponding to the bonus each unit should get for that number of units in the aura (so level 1 grants a 2% damge increase, level 2 a 4% increase, etc.) Then you'll need a trigger akin to this: