Questions about Jass and some other things

1. If you make a local variable, but then never set it to something, then do you still need to null it?
2. When dealing with integers and real, you use 0 to null them right?
3. Is there any way to detect when an unit attacks using Phoenix Fire?
4. Is there a way to detect who gave the unit that buff?

1. I believe no.
2. You do not need to 'nullify' them
3. Event - Unit Receive Damage is a possible solution, although tedious

Event - Unit Receive Damage cannot be used in anyway i know of (since you must specify the unit).....arent there any easier way?

you don't need to nullify number variables at all? doh..

Phoenix Strike should leave a buff, but that is only useful for detecting phoenix strike not owner of caster.

Event - Unit enters playable map area.
Condition -
Action - Trigger - Add ((triggering unit) takes damage) to TRIGGER

Also need to pick all units at the begining. Then you know the damage source. If they have attacks other than pheonix fire...

Yes... if whole map goes around Phoenix Fire without normal attacks or other auto-damage abilities it would work.