User blog comment:Lykrast/CB1 - Celeste, the cosmic mage/@comment-533780-20150326214833/@comment-5686533-20150328155608

It's a refreshing DoT. Buff lasts 4 seconds, DoT lasts 2 seconds. "Damage per attack" is the total damage over 2 seconds. Constantly refreshing for the 4 seconds leaves with an extra 2 seconds from the DoT, so 6 seconds total of damage.