User blog comment:Leafless/Thresh - The Adamant Warden/@comment-7709681-20131029004617

The passive magic damage has two components:

1. A permanent base amount which applies on every attack equal to the total amount of Souls collected

2. A percentual component that increases the more you wait to attack (Max. Damage at ~10s) and is enable for a single attack, for up to a total of