I had a brilliant idea for a friends Pathfinder campaign.
It starts with this-
Sword of Inner Fire
Price 151,315 gp; Slot none; CL 16th; Weight 4 lbs.; Aura strong transmutation [fire]
DESCRIPTION
This +1 flaming burst brilliant energy longsword has a burnished copper hilt and burns with blue and white flame.
In the hands of a mythic wielder, the sword's fire damage bypasses fire resistance and fire immunity. As a swift action, the wielder can expend one use of mythic power to enable the sword of inner fire to damage nonliving creatures (such as constructs and undead) for 1 round, though the sword still can't damage inanimate objects.
A wielder of at least 3rd tier can absorb the sword of inner fire into her body as a swift action, and call it back to hand with another swift action. While the sword is stored in this way, her eyes burn with orange flame and she gains a +5 deflection bonus to AC and a +2 luck bonus on all saving throws.
CONSTRUCTION REQUIREMENTS
Cost 75,815 gp; Feats Craft Magic Arms and Armor, Mythic Crafter; Spells flame strike, gaseous form, instant summons, shield of faith
So you can follow how this idea came about. I was writing an email to my GM about items I wanted to make, so he could think about them in a leisurely fashion. And I wrote-
"Likewise Spellbreaker MA 146 CL 12 and ]Sword of Inner Fire MA 146 CL 16. I particularly like the second, which isn't surprising. Could I make a Sword of Inner Fire not as a sword, which I am not proficient with, but a Dagger, Staff or Shorspear of Inner Fire? I can't see any balance reason to say no, but ur the GM. I think you said at one stage that it should not be a dagger, as that is easily concealable and a sword isn't is, I think, the reason. This isn't past reconsideration, read the description. ]A Trebuchet of Inner Fire is more concealable than a normal dagger."
Then I realise a []A Trebuchet of Inner Fire was an inspired idea.
I looked up trebuchets, specifically a counterweight trebuchet, on wikipedia. If you assume it can shoot a 100kg missile, fairly modest considering the size of shot trebuchets actually fired, then the correct weight for the counterweight is 133x that, or 13.3 tonnes. All up the thing would weigh around 30 tonnes.
According to Wikipedia, a longsword has an average weight of 1.1 to 1.8 kg, say 1.5 kg for a midpoint.
Now, refer back to the magic item description, 1.5 kg of magic item gives a person +5 AC and +2 saves. Now a masterwork counterweight trebuchet will cost more and take longer to make than a longsword. But it weighs 20,000 times as much, so when absorbed into bodies should suffice to give +5 AC and +2 saves to 20,000 people. A substantial army.
Alternatively, it should suffice to give each member of our party + the summoner's eidelon a bonus of-
1/5 x 20,000 x +5= +20,000 to AC
And-
1/5 x 20,000 x +2= +4,000 to saves.
The kink in the plan is it will work for an army, but they all need to be mythic tier 3.
An entirely logical, balanced and reasonable plan imho.