Mana Burn
From Age of Dungeons Wiki
Mana Burn refers to a passive effect which takes place when the player's Mana is below zero. Each tick of natural mana regeneration that occurs while the player's mana is below zero will incur a small loss of life. This effect is greatly accelerated through the use of channeled mana regeneration items.
This state of being below zero mana generally only occurs due to the use of certain dark spells.
