To get the Hadum's Lantern, you need to destroy 1 million monsters in Hadum with a HP below 20%.  BUT How do I find out how much I have?????

If your screen turns red and you hear your heart pouring in game its 20% or less. Make sure to have no pots and no heals and farm at low mobs who cant kill you

You can't see it, it is secret achievement it took me about 42 hours using Reaper