Wouldn't a Marilith with 6 Speed Longswords be awesome!?

[JeminiZero]

You want additional attacks?

Take a Level 12 Wizard, his BAB should be 6. Or better yet make it a Gish with a BAB of at least 11, so that he has 3 iteratives. Buy 12 Mouthpick weapons +1 [LoM] at the sum of 8,000+ gp each.

Now Polymorph into a 12-headed Hydra and wield one mouthpick weapon with each head. Mouthpick weapons specifically allow iterative attacks without requiring the bite weapon to be a primary natural attack, so each head can attack 2-3 times (depending on whether you are a straight wizard or a gish) for 24-36 attacks per round (scaling to 48, if your Gish manages to gain a 4th iterative).

If you really want to go to town, make all your weapons bludgeoning, and cast reach chained Greater Might Wallop on all of them. It should be quite easy to push their effective base damage to colossal size (since Hydras normally wield huge mouthpick weapons). So if you were using e.g. Warhammers, you could deal 6d6 base +6 Str bonus + 1 Enhancement or an average of 28 damage per hit (and gets better if you can cast reach-chain Greater Magic Weapon).