1. Pretty easy...
Trigger:
- Order
- Events
- Unit - UNIT's life becomes Less than REAL
- Conditions
- Actions
- -------- You actions here... --------
It's under the Event > Unit > Life
UNIT = the unit you want to make cast the spell
REAL = the life needed for it to trigger this trigger.
2. There are several ways, depending on the ability.
If it's a point-target ability (means you need to target a point in this ability) then use the actions:
Trigger:
- Actions
- Set Point = (Center of (Playable map area))
- Unit - Order UNIT to Human Blood Mage - Flame Strike Point
- Custom script: call RemoveLocation(udg_Point)
Point = a point variable, needed to be able to remove leaks.
UNIT = The unit you want
Custom Script = to remove leaks which cause lags.
If it's a unit-target ability (means you need to target a unit) then do:
Trigger:
- Unit - Order UNIT to Human Mountain King - Storm Bolt UNIT
Simple enough, right?
If it's an instant, spells like War Stop or Thunder Clap, that instantly cast, use:Trigger:
- Unit - Order UNIT to Human Mountain King - Thunder Clap
Issue order targeting a point
Issue order targeting a unit
Issue order with No Target