So, we take a double crossbow and up size it until it's a ballista. All ballista are just oversized crossbows, after all. And it states a double crossbow is still fired with one hand, you just need two hands to load it.
Now we have a double ballista.
So we'll make it out of aurorium, because it being the size of a medium creature, that thing is gonna get sundered to hell and gone.
Now we give both the upper and lower crossbow +1, Flying, Quick-loading, Self-loading, and reloading. You need to give both flying so that both weapons are considered animated objects.
Oh, so you know a Light Ballista takes two full rounds to load. Self-loading takes that down to one round. Quick-loading takes it down to a move action. Reloading takes it down to a free action.
Now we add deathwand to both the upper and lower crossbow. That gives us room to mount four wands all of which are usable as if in our hand.
Now we add on two oil champers so we can coat the bolts with oil, and two triple weapon capsule retainers filled with quickflame so that two bolts can do 4d6 fire once before needing 8 rounds to reload.
And two gnome sights to reduce range penalties.
OH! and make those bolts tumbling. x1/2 range but +2 damage.
Now, since we have a double weapon and you'll be using two weapon fighting to shoot both the upper and lower crossbow in the same round, we can add Speed to the upper bow.
Now using the Axe of pairs as a base, we can determine that it is a +3 bonus to get an extra attack with your off handed weapon when making a full attack. So we can add the extrapolated WSA Off-handed to the lower bow, giving us an extra off-hand attack.
So you get your base BAB attacks, An off hand attack. An extra speed attack. An extra off-handed attack, and both the upper and lower crossbow are animated objects, so they each get an attack as themselves.
Now, I should point out that Quickloading only gives you space for 100 units of ammo. At 7 bolts a round, you are going last 14 round before you need to take 10 minutes to reload the extra-dimensional ammo holding space. And every time your BAB goes up 5 points and you buy another feat in the two-weapon fighting tree, it's going to burn through your ammunition all the faster.
And I'm sure you can come up with some fun ammo, but I'd still use tumbling bolts. A range of 75 is a small price to pay for 4d6+2 damage.
NOW IT GETS INTERESTING...
Get an underslung Bayonet sword.
Go to Extrapolated Weapon Special Abilities
Get Sorcerer's Hand. (You can NOW fire your RAY attacks through your crossbow and the WSAs add to your ray,and if you don't have ray spells, use wands that fire rays.)
Stack on major WSAs that increase damage: Splitting, Exit Wound. Assassination, that sort of thing
Its also a melee weapon. Enhance the crap out of that Bayonet Sword. I suggest Smoking for the defensive bonuses. Basically, if it's Purple or Blue in the WSA file of the EVD, take a look at it.
Now... go to augmentation.
Look at Just grafts
Look At grafts, Illithid.
Look at weapon graft.
Graft that m-f'er to your left hand.
Now it's an extraordinary ability.
Now it's a natural weapon.
Now it doesn't matter if it's it's own 5' square it's part of you, you're a medium creature, it's in the same square as you now.
Now you buy a necklace of natural weaponry.
Now your NoNW stacks with your crossbow.
Get another +10 in WSAs to stack on the upper crossbow, +10 on the lower crossbow and +10 on the underslung crossbow bayonett.
Go back to just grafts
Go to Grafts, Maug
Get the stone spikes. They add to all natural attacks. Your RAY SPELLS are now a NATURAL ATTACK.
I know it's gonna be grafted to your hand, but give it Flying anyways. No. You won't be able to fly.
Okay. Now that you have your crossbow.
WSAs:
Get Lucky WSA three times, one for each crossbow and the under slung bayonett
Get Doomwarding 3 times.
Reroll until you critical.
Get Blessed so you can confirm criticals when you do hit for a critical.
Note, no DM in his right mind will allow you to make this horror, but I hope it gives you some ideas.
