The Yagnoloth has the following attack entry
Attack: Greatsword +9/+4 melee and claw +20 melee, or greataxe +9/+4 melee and claw +20 melee
Damage: Greatsword 2d6/19-20, greataxe 1d12/x3., claw 1d6+10 plus stunning blow
I do not understand how these figures come to be. The Yagnoloth is a Large Outsider and has 10 HD, so the Yagnoloth should have a base attack of 10. The greatsword total attack bonus given seems to reflect this base attack minus the Size modifier (-1 for Large). But the Yagnoloth has Str 30 (!). There is no errata on the Yagnoloth that I have found.
The Yagnoloth has a special quality:
Muscular Arm: A Yagnoloth's larger arm functions as a primary natural weapon even when it is used to make secondary attacks. This ability negates any secondary attack penalty and allows the Yagnoloth its full Strength bonus with its claw, whether the attack is primary or secondary.
This plus weapon focus (claw) explains the +20 claw attack.
But why only +9/+4 with a greatsword which only does 2d6 damage - no bonus? This seems to be a Medium greatsword as a standard weapon for a Large creature.
Is it correct to assume the entry is wrong and substitute it by the following entry?
Attack: Large longsword +19/+14 and claw +20 melee, or Large battle axe +19/+14 and claw + 20 melee
Damage: Large longsword 2d6+10 and claw 1d6+10 plus stunning blow, or Large battle axe 2d6+10/x3