Elminster's Ecologies: Appendix IIIa
This time-worn tome is written by the sage Elminster, and apparently part of a much larger body of work containing detailed studies of most of the strange creatures from around Faerun.
The appendix seems to refer to newly-discovered variations on normal breeds of creatures. Of particular interest:
"Dense Puddings - a relative of the slimes and molds, this pudding is relatively normal...except when exposed to electricity or fire. When this occurs, it splits into new puddings and can therefore be very dangerous."
"Fire Trolls - a new form of troll thought to have been created by sorcerous Fire Giants for use as servants and guards. They are similar to regular trolls in most respects except for their lava-temperature skin and burning touch. Once they are defeated, they can only be permanently killed by cold or acid."
"Fission Slime - an off-shoot of the slimes and molds, this particular slime will split into new and independent creatures when hit. It is vulnerable to fire, which will kill it permanently."
"Magic Golems - this rare type of golem is formed from pure magical energy and is completely immune to spellcraft as well as enchanted weapons. To my knowledge, only weapons without enchantments have any effects on this creature."
"Marileths - while this is apparently a legitimate form of demon, it is one that only an exceptional few have encountered and survived. The Marileth is a six-armed demon with a human female front half and the back half of a snake. She is incredibly quick and deadly, and on top of her martial prowess with six swords, she casts spells as well. Fighters should beware: in addition to being immune to normal weapons and minor enchantments, this demon also likes to cast Immunity to Magic Weapons...which must be dispelled if a fighter is to have any chance with his armaments."