Aspect - Blood Fever

From AoCWiki

Only one Aspect can be on the Shaman at any one time

Cast time: Instant

5s cooldown to activate/deactivate.

You can have Aspect A running, and provided it has been running for more than 5s, you can click Aspect B which will instantly turn off Aspect A and instantly turn on Aspect B.

Applies a damage bonus 10/12/../../20% damage bonus and a 12%/15%/... healing penalty.

Apparently, this does multiply up combo damage, which is where the bulk of your damage is done.