Swamp nymphs are the most powerful type of nymph in dNetHack. Players attempting to deal with one should consult the main nymph page, especially if they are unfamiliar with nymphs.
Swamp nymphs cast spells in addition to stealing items. If one steals your source of magic resistance, you could be in for a world of hurt.
Swamp nymphs have the additional trait of sometimes "collapsing into a noxious fluid" when badly wounded by an attack. If this happens, the swamp nymph dies immediately, but if the hero made the attack in melee, he/she becomes deathly ill
As a forest pathogen, a fungus can be very destructive.
Its high destructiveness comes from the fact that, unlike
most parasites, it doesn't need to moderate its growth in
order to avoid killing its host, since it will continue to
thrive on the dead material.
[ Adapted from Wikipedia ]