A beautiful flower that emits a gas cloud and metamorphoses those that inhale it into a bogbeast. This is the beauty that Dungeon Master referred to when he said "beware of the beauty that breathes the beast."
Dungeon Master also claims that the metamorphosis mechanism is a spell rather than an exotic nature one and that those that do not reverse the spell soon will remain a bogbeast forever. And adds cryptically that the solution is found by what Eric dislikes the most. The thing that he dislikes the most being staying in the Realm; as when he reaches home through the River That Rains Upside Down he remains a bogbeast until he returns to the Realm.