The elves are descended from Mirkwood elves who never emigrated to Aman
The Lord of the Rings ends with the gradual disappearance of fantastic creatures from the world in order to make space for humans, and Thranduil's kingdom is said to persist well into the Fourth Age without any information on what happens to them afterwards. It's not much of a stretch to assume the events of this movie is a continuation of the above. Liz' ultimate suffering as described by the Angel of Death will be the loss of her children.
She is specifically described as being out of everyone on earth, the one that will "suffer the most" when Hellboy inevitably leads to the destruction of humanity. Your own injury and/or death are nothing compared to losing your children.- It might refer to the death of Hellboy himself. In the comics it's suggested that Hellboy's inevitable death (everything dies) is what kick-starts the apocalypse. The death of a spouse is one of the most soul-destroying pains a person can go through.
- Or one's child. Or both.
- I thought the Angel was referring to the pain of watching the love of her life turn into an unrecognizable, soulless monster that triggers the apocalypse. And depending on how much the kids take after Dad, they could become monsters, too.
- Or the Angel of Death, like Rasputin in the previous film, think that they can make Hellboy's destroy the world destiny happen if they just keep repeating it. Some people just want to be right. Maybe Liz' ultimate suffering consists of Hellboy trying to comfort Abe over the loss of Nuala, resulting in years of drunken duets. The horrors.
