thxCreate 3 different combats, call them for example combat1, combat2 and combat3.
Then use addEvent to execute the combats.
http://otland.net/threads/creating-layered-spells-on-9-8.224175/#post-2156111
You can also use the spellcreator tool
http://otland.net/threads/spellcreator-a-graphical-spell-creation-enviroment.160371/
local combatFire = createCombatObject()
local combatDeath = createCombatObject()
local combatIce = createCombatObject()
function onCastSpell(cid, var)
return doCombat(cid, combatFire, var), doCombat(cid, combatDeath, var), doCombat(cid, combatIce, var)
end