Needs More Whammy Bar Achievement in Halo: The Master Chief Collection

The Prophet Birthday Skull is a new skull modifier introduced in Halo 2: Anniversary which causes each and every smack on the Prophet of Regret’s face to be accompanied by Steve Vai guitar riffs and flamboyant lightening bolts.

As such, all you have to do is activate this skull in the Campaign lobby and then load up the aforementioned mission on any difficulty setting. Once you reach Regret’s temple towards the end of the mission, continue as you normally would in defeating the Prophet of Regret and the achievement will unlock after he has been defeated.