Need help designing a maguffin / WMD

[Angel Hunter D]

So, I'm currently GMing a campaign that's heavily influenced by the .hack// series that is on hold for summer and I want to start developing the endgame for the adventure. I've been making scenarios up as we go so far, drawing from a bunch of different influences but the overall plot has been fleeing from and trying to find a way to defeat a powerful demi-god of the Dark Tapestry.

Where I need some help is that at the end of their quest they'll receive a powerful tool to defeat the demi-god from another powerful, but sealed, god. I want them to have their climactic showdown around level 18, but I've only played some society and low level modules and have no idea what kind of gear they should have at those levels.

TL;DR - Making a super-weapon for a final confrontation at lvl 18, how good should it be to feel better than normal but not make the players without it feel useless.

[the David]

Well, a MacGuffin actually doesn't do anything, beyond being a big plot element. it's like the unobtainium in Avatar. It doesn't really matter what it is, as long as everyone wants to have it.

As for how much your weapon should cost, no more than half of what a 18th level character should have according to the wealth by level table, or 265000 GP. That's a +5 weapon with +5 worth of abilities on top of that. Adventurepaths sometimes give baneweapons for this purpose.

Alternatively, if you divide the maximum of +10 (effectively) on a weapon over the 20 levels you can get in Pathfinder, you wind up with a +9 (effectively) at level 18.

[cnetarian]

Are you tied to having the super weapon be a regular weapon, or would a deity destroying weapon like lyrta spores which gestate into a rapidly reproducing deitivorous (deity eating) fungus that does exponentially increasing damage to the deity (1d20 damage on the first round, 2d20 on the second round, 4 d20 on the 3rd round, 8d20 on the 4th round and so on - only one dose of spores is available) and can be applied by any character work for the climactic show down? When dealing with killing deities I prefer to give the players one-shot weapons just so that they are less likely to use them on the wrong deities.

[Angel Hunter D]

The weapon is going to be normal in most cases, but when used with a paired bracelet on another player it'll inflict negative levels to knock the god down to their level.

as for them using it on the wrong deity, they're supposed to give it back after and the monk is really big on doing the right thing.

[My Self]

Perhaps you have your superweapon as a team-boost item? Instead of a weapon that can simply slay a god, how about a weapon that can raise an army that can slay a god? Maybe with a certain dilution thing-you get some sort of favored enemy (Deity) that is either around +10 for a single person, or could be divined up to a group for +6, or an army for +4. And it comes with the favored defense thing or whatever.

[Angel Hunter D]

interesting idea, i like it but i don't think it'll fit in this theme.
In the .hack// games the mechanic was pound on the boss a bit, break his guard then hit him with your unique ability and BOOM, weaker and able to be damaged. Fighting a demi-god i was thinking that the pound for a bit could be removed if i made the ability take a few parts (hit with 1-2 ranged touch attacks and a blow from the weapon).

I was more interested in how powerful weapons should be at 18 and then i was going to add the mechanic on top.