Setting aside the two attacks bit for a moment, I also think Belkar has too many feats if he does have Spring Attack. For Spring Attack, he needs to have Dodge and Mobility as pre-reques.
In his statblock he has as listed:
Craft Disturbing Mental Image
Great Cleave
Improved Sunder
Power Attack (prerequisite for Improved Sunder)
Two-Weapon Pounce
If we include (and as has now been updated ) Spring Attack and the prereques:
Spring Attack
Dodge
Mobility
That's eight feats. At lvl 15 he should have six feats, correct? OK, as funny as it is, Craft Disturbing Mental Image can go on the chopping block as a 'real' feat. Maybe he got it for free or sumthin.
There's still one too many feats unless I am massively messing up somewhere.
As I look about, I see that Rangers can choose Two Weapon Pounce if they meet certain requirements. But it doesn't appear as if they can choose it as part of their improved weapon style.
So does something go on the chopping block here? Or do we fold in Two Weapon Pounce as an Alternative Class Feature of Rangers for Belkar?
We could also possibly knock out Great Cleave if all we are going on is Belkar's comment about "I'm gonna try for two now." After all, just because he could try doesn't mean he could succeed. And on-screen evidence should trump attempted non-screen evidence.
And all Improved Sunder lets one do is make an attack against a Hydra's head without an Attack of Opportunity. That could be explained away as the Hydra just missed and Rich didn't depict it in the combat explicitly.
Is there evidence for Great Cleave later on in the comic? Or Improved Sunder? If so, Alternate Class Feature for Two Weapon Pounce could be our only alternative. Though I may be missing something pretty big, due to my rust.
ETA::: We could also always open up the can of worms of One Flaw Equals One Feat variant rule. And if any character in the OotS has feat flaws it'd be Belkar.
For instance, Inattentive [You are particularly unaware of your surroundings --- You take a -4 penalty on Listen checks and Spot checks]would certainly work. So to could Weak Will [You are highly suggestible and easily duped --- You take a -3 penalty on Will saves]. Either of them would help explain how he seems to be so lacking in Wisdom, even though he looks to have no worse than a 9 due to various reasons that are better not rehashed for the thousandth time.
Listed just as examples, not as suggestions to add it to the block.