I've got a request for the many people here better at Op than me.

[tonberrian]

It also specifies natural weapons, so you could polymorph first. How does Flurry or TWF interact with polymorphing into something else?

That's an idea.

Totemist//Arcane Spellcasting Thingy

Polymorph into, say, a kraken, and use the Totemist soulmelds for a bunch more natural attacks other than tentacles. Use Arcane Strike to power all of them simultaneously.

Bonus points if you can fit Warshaper and Raging Mongoose in there too.