So I played a Death Worshipper then threw out a fatty in my defense zone that iced 12-15 of my opponent's 3/3 flying Spirits and her ability never activated. Kinda sucked cause I was counting on her strength to skyrocket.
I asked my opponent and he suggested that it could be that his Spirits didn't go to the graveyard (they were brought into play by that Xi card - sorry, I'm still learning names). Assuming this isn't a bug...
(1) My primary suggestion is to change this so that the Death Worshipper will activate from these. They are an enemy character, they are being killed, one would expect the ability to activate.
(2) If for some reason she really isn't supposed to activate from these, the card text should be changed so other players in my situation aren't caught off guard. Nothing in the card text mentions the need for opponent's character to go to the graveyard.