If I'm not mistaken, you can kill just about any monster in Labyrinth Lord as long as you have three things:
2) An illusionist who can cast Hypnotic Pattern (which means they only need to be 3rd level)
3) Another guy or gal with a weapon that can damage the monster
Here's how it works:
You get initiative, the illusionist casts Hypnotic Pattern. What does Hypnotic Pattern do? It is described thusly, "A twisting pattern of subtle, shifting colors weaves through the air, fascinating creatures within its area of 30' square, centered on the caster. A total of 24 HD of creatures are affected, in any combination (twelve 2 HD creatures, four 5 HD and one 4 HD creature, etc.). Affected creatures become fascinated by the pattern of colors and remain motionless, dazed, for as many rounds as the caster concentrates on the spell and makes no other action."
What is noticeable is the lack of a Saving Throw. If the caster gets the spell off, BAM! 24 HD monster is staring at the pattern like a mook, completely helpless. And the duration lasts for as long as the caster cares to keep it up, giving the second person enough time to wail on the beast until it dies.
(Edited to add: Hypnotic Pattern is in the AEC.)