Scripts

After each battle, you can use the following code:

function rndcast()
	while 1 do
		SetGameVar('spell', random(5))
		local index = GetLastSavedCombatIndex()
		while index == GetLastSavedCombatIndex() do
			sleep(10)
		end
	end
end
startThread(rndcast)

And in the combat script, replace the line:
cast = GetGameVar('spell')+0
with the line:
cast = random(5)
Yes, and random(5) will return a random number from 0 to 4. That is, random(n) returns a random number from 0 to n-1.