Ravage enemy with a spinning attack to deal [x] Magic Damage and increase your damage against them by 20%.

Also causes Major Defile, reducing the effectiveness of healing on the enemy by 30% for 6 seconds.

This is how it is displayed in game. Why do people assume that the 20% damage buff works only for 6 seconds when it's paired with "Deal x magic damage". To me, I read that and it clearly says "Indefinite +20% damage against a single target". To clear up the confusion they could simply put the following:

Ravage enemy with a spinning attack to deal [x] Magic Damage and increase your damage against them by 20% for 6 seconds.

Also causes Major Defile, reducing the effectiveness of healing on the enemy by 30% for 6 seconds.

Something like this. I'll have to go test it out to see if it's 6 seconds (as everyone says), of it's a perma-buff as the tool-tip implies.