So, you got astral construct:
Description: Coalescing ectoplasm takes the form you desire.
This power creates one 1st-level astral construct of solidified ectoplasm that attacks your enemies. It appears where you designate and acts immediately, on your turn. It attacks your opponents to the best of its ability. As a free action, you can mentally direct it not to attack, to attack particular enemies, or to perform other actions. The astral construct acts normally on the last round of the power’s duration and dissipates at the end of its turn. Astral constructs are not summoned; they are created on the plane you inhabit (using ectoplasm drawn from the Astral Plane). Thus, they are not subject to effects that hedge out or otherwise affect outsiders; they are constructs, not outsiders. You can have only one astral construct shaped at any one time. If you shape another astral construct, any previous construct dissipates. (The exception is if you are a 5th-level ectopic adept, which gives you the ability to create another astral construct while you have one active).
Augment: For every 2 additional power points you spend, the level of the astral construct increases by one.
Notice it says, takes the form you desire.
Then you got the advanced menu B option:
Metaphysical Construct (Ex): The astral construct's body becomes a +3 psionic weapon. This provides a +3 enhancement bonus on attack and damage rolls made with its slam attacks. While the power is in effect, the construct's body shimmers and arcs with static electricity. (A good choice, not an amazing choice, but a good choice.)
Now, while it gives you a +3 enhancement bonus on it's slam attacks, it says specifically the ENTIRE BODY is a +3 psionic weapon.
Example Constructs:
1ST-LEVEL ASTRAL CONSTRUCT CR 1/2
N Small construct
Now, We show that the Astral Construct can be as small as small size.
So, is there any reason that I cannot make as a DC 15 crafting check (just to be absolutely sure we're on the up and up) to create my Astral Construct as say... a two handed sword? Even if you say that the astral construct cannot be created with less than minimal body mass, there is no reason my astral construct cannot be a small bug like creature that clings to my back with a very long tube-like arm that ends in a two handed sword. Yes, I would have to carry said creature (weight of 25 lbs).
So, lets say I make my small creature using weaponcrafting skill DC 15 check. I mold his legs into two tubes that run down my arms and into my hands and form the two-handed sword. I have to have a custom made saddle in order to have him "ride" me. He still has his arms free, so he can still make Full-round attacks (he has his move action, because I provide his movement) and if needed, I can order him to "spur" me, (unskilled DC 15 ride check) so I take 2 HP damage, and can move an extra +10 feet.
And, of course, I get a two-handed +1,+3,+5 weapon, depending on which menu item I can pay for.
Thoughts? Possible?
Also, Can I just skip the whole having my AC mount me jazz and just go straight to "It's a +3 sword" and skip the whole it's riding on my back with tube feet? I know it will lose any attacks it would have, but there are reasons you might not want a ball of astral snot on your back with wiggly arms turning into a sword.
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Now, additional question:
I can summon the construct to look like anything I want. I can give the construct magic items to use (if it could use it) if I wanted to. can I Summon it into a square where I am holding a Graft and have it form around the graft?