Sorrowsworn demons: highly dangerous, 18 RHD fiends who for some reason look like starving werebat goths. It's kinda neat, though.
Ability scores are predictably high. The lowest one, 17 dexterity, is still quite respectable for a Large creature, whereas the highest stat is an impressive 32 constitution. Strength is not far below constitution, and the mental stats are somewhere in between. 80 ft. fly speed is cool, poor maneuverability less so.
+16 natural armor is quite high, DR 10/cold iron and good is very unlikely to be overcome, immunity to electricity and poison are good to have, and resistance 10 to acid, cold, and fire is obviously useful too, and Telepathy is icing. SR 25 is somewhat less desirable, as it complicates in-combat healing and buffing. Improved Initiative and Improved Toughness for free are neat, though. All in all, not a lot of unexpected traits here.
The demon's special abilities, on the other hand, are more interesting. Aura of Loss is your basic disruptive aura: it reduces saves, attack rolls, and skill checks, and complicates spellcasting. Not that the average wizard is likely to care much (DC 29 is taken care off by 21 ranks, 12 constitution, and a +5 concentration item), but it may be an issue for whatever foes you face that didn't invest in concentration. Do note that it's not friendly, though.
SLAs are, again, reasonably standard. At-will Greater Teleport, Detect Magic, Nondetection, and Invisibility, 3/day Greater Dispel Magic, Touch of Idiocy, and Unholy Blight, and 1/day Feeblemind, Mind Fog, Plane Shift, and Weird. There's some utility there, some save-or-loses, and some useless crap.
Strong Willed is a boring ability that adds a small bonus to the sorrowsworn's already good saves vs. mind-affecting effects. Mind Reading is a unique ability that doesn't take actions, but has uses both in and out of combat. If combined with the Aura of Loss, it imposes a -2 penalty on creature's saves against the demon's Whispers of Loss.
Said ability is also a free action (obviously limited to 1/round), and can either stun a foe for 2 rounds, daze it for 3, or confuse it for 5 rounds. A foe who saves against one effect is immune to it for 24 hours, but can still be affected by the others. The ability is, however, mind-affecting, meaning it's not impossible to block.
That last bit is what keeps the sorrowsworn demon from getting +1 LA. It's got neat tricks, but against any of the many foes that can resist mind-affecting attacks it'll struggle to keep up. The outsider RHD and array of tricks against foes that aren't qualify it for a LA above -0, though.