[Phanx]

Originally Posted by semlar I'm not sure if you're suggesting this or asking how, but basically what you would do is on that event make a for loop from 1 to MAX_BOSS_FRAMES, check if UnitGUID('boss'..i) exists, and if it does extract the npc ID and compare it to the one in your list.

local BossesToCheck = {
   [68476] = true, -- Horridon
   [69017] = true, -- Primordius
}

local MyAddon = CreateFrame("Frame")
MyAddon:RegisterEvent("INSTANCE_ENCOUNTER_ENGAGE_UNIT")
MyAddon:SetScript("OnEvent", function(self, event, ...)
   for i = 1, MAX_BOSS_FRAMES do
      local guid = UnitGUID("boss"..i)
      if guid then
         local mobid = tonumber(strsub(guid, 6, 10), 16)
         if BossesToCheck[mobid] then
            -- You are engaged with one of the bosses on your list.
            return
         end
      end
   end
   -- If you didn't return out by now, you're not engaged with any of the listed bosses.
end)