[LUA] Simple Boss script

[alj03]

I got it working and all, but it doesnt say what it's ment to say when i enter combat. Also spells dont work..

[Devilsadvocate]

function XXX_FireBall(pUnit, Event) 
pUnit:FullCastSpellOnTarget(31620, pUnit:GetRandomPlayer(7)) 
end

function XXX_FireVolley(pUnit, Event) 
pUnit:CastSpell(37109, pUnit:GetRandomPlayer(0)) 
end

function XXX_Transform(pUnit, Event) 
if pUnit:GetHealthPct() < 75 then 
pUnit:RemoveEvents(); 
pUnit:FullCastSpell(0)
pUnit:SetModel(YYYY)
end 
end

Ok correct me if i'm wrong seeing as im not a very advanced lua scripter but aren't these supposed to be registered via " pUnit:RegisterEvent("Event", Time, 0) ?" Otherwise how is the script gonna know when to call the functions?