Lua lever spawn monster

function onUse(cid, item, fromPosition, itemEx, toPosition)
    local fromPos = {x = toPosition.x - 10, y = toPosition.y - 10, z = toPosition.z}
    local toPos = {x = toPosition.x + 10, y = toPosition.y + 10, z = toPosition.z}

    for x = fromPos.x, toPos.x do
        for y = fromPos.y, toPos.y do
            for z = fromPos.z, toPos.z do
                local tile = Tile(x, y, z)
                if tile then -- check if tile exists
                    local creature = tile:getTopCreature() -- get top creature
                    local monster = Monster(creature) -- change Creature to Monster (check if it's monster)
                    if monster and monster:getName() == "Ferumbras" then
                        doSendMagicEffect(getThingPos(cid), CONST_ME_POFF)
                        doPlayerSendCancel(cid, "You need to kill Ferumbras first before you can summen one again.")
                        return true
                    end
                end
            end
        end
    end

    doSummonCreature("Ferumbras", {x = toPosition.x - 1, y = toPosition.y + 1, z = toPosition.z})
    doPlayerSendTextMessage(cid, MESSAGE_INFO_DESCR, "You have summened Ferumbras.")
    doSendMagicEffect(getThingPos(cid), CONST_ME_MAGIC_BLUE)

    return true
end