custom spell trigger help

Okay, this time it's a custom spell effect.

I found out a way to make blizzard heal since you can't really change the targets around, and it doesn't work with - damage values, BUT I'm still a novice trigger man so I don't know how to get the effect I want just yet... But I know how I need it to get done.

what I need is a trigger that'll detect when my custom blizz is cast, then summon up an invisible unit to cast a spell right in the middle of it's AoE before it disappears. Sounds simple enough, but I don't have any idea how to go about it...

any suggestions?

ps. I also probably need that range-check trigger thing too...

use redskulls editor, make the dmd values negative, and u got heal.

first thing is I only want it to heal alied units.

second thing is I've tried negative values with blizz before. It just doesn't work for whatever reason.

Which is why I need to do this other thing... Or atleast I think that's the way around it.

Basicly what I want to do is summon up an invisible unit that has healing ward and have it cast and inviso ward right in the middle of my custom blizz's aoe to simulate the effect I want. It should work fine in theory (0 damage blizz doesn't hurt or heal, but shows the animation like I want, is targetable, comes down in waves, makes the caster channel, etc etc etc... and Healing ward heals every X seconds so it'll take care of the healing part and match the waves of blizz, or atleast come close enogh..)

So here's the trigger I need.

-unit casts custom blizz.

-inviso unit spawns/is summoned/created/whatever
-Inviso unit is forced to cast modified inviso healing ward inside custom blizz's aoe.
-inviso unit unsummons.

dont know how to do this on my own.

Otherwise you could base the spell of inferno, like in dota.