@JeremyECrawford Is the extra 1d8 damage from the Ranger's Colossus Slayer mandatory if the conditions are met? (For example, friendly fire)

— Kooper Koushiro (@KooperKoushiro) April 28, 2016

You choose whether to deal the extra damage of Colossus Slayer. #DnD https://t.co/ywjZaDQfmh

— Jeremy Crawford (@JeremyECrawford) May 3, 2016