Well, the problem is quite delicate. First of all because you need to know when the shards hit the units. I came with a relative solution (durations can be modified, that's why I gave no numeric value for it, you can test with different values till you find that they are ok).
Trigger 1
Event - An Unit Starts The Effect of an Ability
Conditions - (Ability Being Cast) equal to BlizzChill
Actions - set BlizzCast = (Triggering Unit)
- set BlizzPoint = (Target Point of Ability Being Cast)
- Wait X seconds
- Turn on Trigger 2
Trigger 2
Event - Every X seconds
Actions - Pick Up Every Unit Within Y from BlizzPoint and do actions
-> Create 1 Dummy for (Owner of BlizzCast)
-> Add FrostNovaBlizz to (Last Created Unit)
-> Add 1.00 seconds Expiration Timer to (last created unit)
-> Order (Last Created Unit) to Undead - Lich - Frost Nova (Picked Unit)
Trigger 3
Event - BlizzCast Stops Casting an Ability
Conditions - (Ability Being Cast) equal to BlizzChill
Actions - Turn Trigger 2 Off
- set BlizzCast = No Unit
Now, let's discuss certain stuff. BlizzChill is your blizzard ability you enchance. FrostNovaBlizz is just a Frost Nova ability for the dummy unit which does 0 damage and you set the duration to how long you want the chill to persist.
X is the duration between two waves of the blizzard.
Y is the area of blizzard spell.
BlizzCast is an unit variable.
BlizzPoint is a point variable.
That should do it!
~Daelin