The Holl is a creature you do not want find in this game. It pops out of a trunk in a tower, while you're looking for the prince/princess during a tower rescue in the Forest. Once you make your choice of towers, the end result is unavoidable. Sorry. Go get healed, and don't guess that tower location next time, because until you guess correctly, the Holl will always be in the same two towers out of the five.
The Holl will always be the opposite gender of your character. It's half-troll and half-human, and it attacks you with unavoidable ferocity--and, dare we say it, horribly repressed lust--and drains your HP to 20% of where it was before you met it. Experimentation by blah and injektilo* in Test realm has shown that repeated exposure to the Holl without healing will continue to lower your HP by 80% each time, even down to zero HP, but you will not be "dead" and may continue to roam the forest. However, since your HP won't qualify as enough to do battle, you won't encounter any Forest monsters, just Forest events.