Jormungantic

Book of the dead is useless unless you build book of thoth.

Agreed. And for a god that, outside of his ult, doesn't have mobility and has a share of the largest hitbox, you can expect to take a good amount of damage. Full offensive items are probably not suggested except situationally Magus, especially when you double-up on penetration inefficiency due to having both Spear of the Magus and Obsidian Shard at the same time.

Nemean is really only good when you're facing basic attackers, with emphasis to counter crit builds, or at least to counter multiple basic attackers. It shouldn't be a stock / core item that doesn't show any other situational item options.

Sorry, it's my first build I've posted on SmiteFire, Not 100% sure on how it works atm, But this build works particularly well in Joust.

I'd drop the blessing for arena and go with something more like this:

Shoes of Focus, Void Stone, Breastplate of Valor, Spear of the Magus, situational items like Hide of the Nemean Lion (anti-crit), Midgardian Mail, Winged Blade, Pestilence, etc. Basically build him like a bruiser guardian because he'll be in the enemy's faces and needs some protections to keep him alive. As for the build, eh. Spear of the Magus and Obsidian Shard shouldn't really be in the same build. Plus Book of the Dead is pretty much useless without more mana items and Hide of the Urchin already provides a shield when fully stacked. The build has no aura items for support (e.g. Sovereignty, void, Gauntlet of Thebes, etc), and doesn't have any counter-defense against a solo lane opponent, so I can't recommend it at all.