spell/poison stacking

[Grundy]

anyone know how to make poisons stack with itself? i know you can change the stacking type to attack speed, movement speed, damage, and kill unit, but thats not exactly what i want. that makes it stackable if multiple units use it on the same target. im looking for something more like that vicious mucus thing that the one razorback hero has in DOTA where he casts it on a unit and it takes away 1 armor, and slows movement speed by like 10% and he can cast it up to 4 times on the same unit to give it -4 armor and -40% movement speed. and thats the same unit casting the same spell on the same target. changing stacking types does not let you do that.

and no im not trying to copy anything from dota, i have my own idea, but it would be soooo much easier if i knew how they did that spell in dota.

 

[grundy1]

i forgot something, the buff changes too. the buff tells you how many times the spell has been cast.
ex:
spell called slow poison (casted spell not passive weapon effect)
10 second duration, 1 second cooldown, can be cast up to 4 times.
cast it once on a unit
it has Slow Poison 1 buff
cast it again on the same unit
it has Slow Poison 2 buff
etc... untill it has Slow Poison 4 buff
then the first cast wears off and it has Slow Poison 3 buff
and keeps going down untill it gets to Slow Poison 1 and then the buff is gone.

 

[Slapshot136]

make a trigger
if ability is cast
conditions target unit has buff level 1
actions create dummy caster, order dummy caster to cast (same base spell of what ur using) but a higher level (2)