OK, starting with the yugoloths:
Baernaloth (Outsider, CR 9?)
This tall, lanky creature has long, gangly limbs. Its head is huge with large curving horns, and its mouth looks like that of a skeletal horse, with skin stretched over it. Its gray skin drips with pus, and its glazed, glassy yellow eyes ooze a revolting liquid.
Outcast yugoloths, rumored to be progenitors of the race, baernaloths are demented masters of pain. A baernaloth has the ability to reopen and close wounds it has inflicted, and has a host of spell-like abilities.
Originally found in Planes of Conflict.
I have given this alot of thought, and I am convinced that now is the time to attempt to grant these guys the stats to match their legendary power. They are suppost to be the creators of the yugoloth race, and rumored to have created all the fiends and the Blood War. They are supposedly near-deity in status. And yet, they aren't much tougher than a mezzoloth!
The way I see it, we have several options to rectify this problem.
1.) Stick with the baernaloth as written, but create a greater version ("ancient baernaloth" or somesuch), advanced to CR 20, similar to many of the monster entries in recent WOTC products. For an example, see the nycaloth commander in MMIII.
2.) Ditch the CR 9 version altogether, and simply power 'em up so that the weakest is on par with a balor or pit fiend. There is precedent for this...check out the power inflation of the arcanaloth between 2E and 3E.
3.) Do nothing, stick with the CR 9 version, and continue to read the streams of negative comments on messageboards about how they are too weak.
Dergholoth (Outsider, CR 10?)
Dergholoths have round bodies with five arms and three legs with insect-like heads. They attack with claws and manufactured weapons in any combination. They have a feeblemind special ability and spell-like abilities.
Originally found in the first edition Monster Manual 2.
Gacholoth (Outsider, CR 9)
This semi-humanoid creature has ebony black skin, and four long, powerful legs tipped with three sharp claws. Its muscular torso has two arms that end in sharply-clawed, four-fingered hands. Its triangular ears flare back from its bony skull, and its hairline recedes into a thick patch of dark hair. Its eyes are cold and inhuman. The creature’s sharp fangs protrude from its waiting mouth.
Gacholoths serve as infiltrators and saboteurs, using their great speed and manueverability to their advantage. Their claw attacks deal additional acid damage and have a frigtful presence ability, as well as a variety of spell-like abilities. Additionally, they can walk on walls and ceilings as easily as on the ground.
Originally found in Dungeon Magazine #49 and Monstrous Compendium Annual Four.
Guardian Yugoloths: These are not true yugoloths, just as bebliths are not true tanar'ri and kytons are not true baatezu. These creatures were created by the yugoloths as lesser servants for their mortal allies, and to serve in their stead when powerful wizards call upon them for favors. They are tied to a treasure, and must remain within 180 feet of it. All three versions have a cone of fire breath weapon, immunity to polymorph and mind-affecting abilities, and are immune to one or more forms of attack, randomly determined (including acid, cold, electricity, fire, sonic) or gains a different defensive special quality (such as damage reduction /slashing or /silver). Additionally, they have the ability to attempt to break the summoning, allowing them to attack the summoner.
Originally found in the first edition Fiend Folio and in the second edition Monstrous Manual.
Guardian, Least (Outsider, CR 3-5)
Although they can vary in size and form, most are horned and frog-like.
Guardian, Lesser (Outsider, CR 4-6)
Although they can vary in size and form, most are ape- or boar-like.
Guardian, Greater (Outsider, CR 5-7)
Looks like a gigantic, winged bear with ram horns protruding from its forehead, and talons for hands. Can use a suggestion spell-like ability at will.
Hydroloth (Outsider, CR 8?)
Hydroloths look like froglike humanoids with warty yellow skin. They are elite forces used for amphibious attacks and ambushes. They are immune to the effects of the River Styx. They have a spit attack that causes sleep, spell-like abilities, and can summon a Huge water elemental. They can also glide through the air using their skin flaps, but cannot truly fly.
Originally found in the first edition Monster Manual 2.
The hydroloth and dergholoth were supposed to be weaker than the mezzoloth, yet the 3.5 version of the mezzoloth is CR 6, whereas the conversions of the other two are higher. Additionally, the hydroloth is supposed to be better than the dergholoth. Although it has less Hit Dice, it had a higher XP Value and the flavor text indicates their superiority.