So the thing is this:
- Save 3 lumber at any time
- Put turrets that will kill elemental you wish to spawn at the bottom of the map
- Summon that elemental and when he's at the half way to the turrets summon another one
- After the 1st one dies you can summon another same 2nd sumoned elemental
I think this happens cause of "unit dies" event with condition "which unit dies" and then checks for reserches missing in reserch center and elemental kills...
So if lvl 2 fire is missing and you just killed it you will get fire level 3, and if lvl 2 earth is the 2nd one and it isn't already killed it will appear there twice...
I was programming wc3 long time ago but im 90% sure this is it..
Greets