You've seen hell hounds, now get ready for daemon dogs!
Canoloths are 6 RHD evil outsiders of medium size. Their ability scores are more-or-less what you'd expect: high strength, high constitution, low intelligence, average charisma and dexterity. Notably, however, they have 17 wisdom.
Being yugoloths, they get a bunch of assorted energy resistances, DR 5/good, spell resistance, immunities to poison and acid, and Telepathy.
Important to note: canoloths do not have eyes, and are in fact blind beyond their 40 ft. blindsight range. Negating one of its hearing and smell greatly reduces its ability to operate, negating both blinds it completely. This is a pretty big drawback, for obvious reasons. Mindsight can alleviate the issue a bit, but it's still problematic.
In terms of attacks, canoloths have a natural tongue attack with 20 ft. (!) reach, that deals 1d4 damage and can also cause paralysis. Notably, this paralysis lasts for minutes, meaning it completely removes foes from combat. They also get a more conventional bite, which deals a hefty 2d6 damage instead (and, in open defiance of common sense, can be occupied by a mouthpick weapon while still allowing tongue attacks).
Anything hit by the canoloth's tongue attack, whether paralyzed or not, can potentially be grappled using Improved Grab. If the attempt succeeds, the creature is immediately pulled into the canoloth's mouth and bitten.
Finally, there's the magical abilities. The SLAs are at-will Cause Fear, Detect Good, Detect Magic, and Desecrate, providing some minor utility that becomes major utility if your party has a necromancer. There's also Summon Yugoloth, which allows the canoloth to once per day summon either a mezzoloth or 1d3 canoloths, with a 40% chance of success.
Honestly, if the canoloth was humanoid in shape, I'd assign it +1 in a heartbeat. As they are right now, I'm less sure about it. The paralyzing tongue is an amazing save-or-lose with great reach, and the summoning ability is pretty major (if unreliable), but being completely blind and without opposable thumbs can be a pretty large drawback. In the end, +0 is a good compromise.