Is the attack entry of the Yagnoloth (MM 2, p. 203) in error?

Question

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

Answer 1

Don't assume it's wrong!

The yagnoloth's Combat entry begins by saying

A yagnoloth always attacks with both arms in melee. It wields a great axe or greatsword with its smaller arm, but that arm is fairly weak (Str 10) and the yagnoloth does not receive any Strength bonus when using it. (Monster Manual 204)

So, yeah, the creature's attacks are accurate. Apparently, the rest of the creature's body besides that one arm is also Strength 30 since its Jump skill modifier is accurate. (Yes, I did the pre-revision skill points math, and the creature's skill points were legit before their 3.5 adjustment by the Play More update booklet. (They're legit after, too.) Prior to the 3.5 revision, a creature received no modifier to its Jump skill checks for speed; instead, a creature with a higher or lower speed just cleared more or less distance when it leaps. I don't say it often, but good on 3.5 revision architect Andy Collins for this change.)

This is extremely easy to miss. A Monster Manual II Combat entry has caused confusion before.

By the way, the creature's using a greatsword (or, as the Combat entry says, a greataxe) because, pre-revision, a greatsword really was just a Large creature's longsword. The 3.5 revision changed things so that, instead of just a greatsword, a Large creature uses a longsword designed for a Large creature. In a 3.5 campaign a yagnoloth should be wielding that bigger longsword rather than suffering a penalty for using, like, a greatsword designed for a Medium creature.