local T = {}
local function OnCombat(pUnit, event, pAttacker)
    T[tostring(pUnit)] = CreateLuaEvent(function() HPCheck(pUnit) end, 5000, 17280)
end

local function HPCheck(pUnit)
    if(pUnit:GetHealthPct() <= 20) then
        for k,target in pairs(pUnit:GetInRangePlayers()) do
            target:CastSpell(9220)
        end
        if(T[tostring(pUnit)]) then
            DestroyLuaEvent(T[tostring(pUnit)])
        end
    end
end

do
    local QUERY = WorldDBQuery("SELECT Entry FROM creature_proto WHERE boss = 1")
    for i = 1, QUERY:GetRowCount() do
        RegisterUnitEvent(QUERY:GetColumn(0):GetLong(), 1, OnCombat)
    end
end