Talk:N'kuhana's Opinion/@comment-24.70.207.233-20190428033323/@comment-70.26.188.164-20190430195828

"Store 100% (+100% per stack) of healing as Soul Energy. After your Soul Energy reaches 10% of your maximum health, fire a skull that deals 250% of your Soul Energy as damage."

So, it looks the amount of healing needed to fire off a flaming skull of death is less and less with each stack.

Source: https://riskofrain.fandom.com/wiki/Item_(Risk_of_Rain_2)