Shadowknight Spell

[Evilary]

So I was making upgrades for my Shadowknight on my Alchemist and I read the description of the spells to try to decide if I want to upgrade it. I don't understand the Pestilence based on the description. Everything says it applies damage to the caster. I do not see anything in the description that is beneficial to the caster unless they just like taking extra damage??? Is this a suicide spell or something?

 

[Observing]

It puts a "buff" on an enemy. That "buff" deals damage to whatever it is on. If the enemy dies, the buff is put on another enemy

 

[Evilary]

A buff on the enemy is what I thought it should do. The description sadly says it's on the caster. That's where the confusion comes in.