The new Boss Fight Event isn't going very smoothly. Many can't initiate it and those who can are left wondering how they are going to get the last two achievements. Consumable items do not appear to be dropping unless you have an active Boss Fight and there are no Shotgun Blasts on the Free Gift Page. Those who were doing the Boss Fight before it was pulled lost progress along with consumables. It makes no sense to me why we have to play hide and seek with this thing. Having to initiate a Boss Fight by icing other players seems a bit too complicated. There doesn't appear to be a pattern and I've personally blown through over 10K stamina in an attempt to get the fight again. Hopefully it's just buggy right now and it will be better tomorrow. If there was a Customer Support FAQ, it would probably look something like this.
Assassin: The Raven FAQ