Help with high level gestalt one-shot build.

[Anger Nogar]

We are doing a lvl 16 gestalt one-shot and for the silly literalism of it I have decided to try and make a one-shot (sort of) build.

At the moment I am considering Elf Musket Master (Gunslinger) 6/Eldritch Knight 10 | Arcane Gun (Wizard) 6/Eldritch Archer (Magus) 10

Traits: Magical Knack, Magical Lineage (Shocking Grasp)

The idea is to precast a named bullet and intensified shocking grasp and then when the combat starts to vital strike both barrels of your musket, discharging the shocking grasp, scoring a critical thanks to named bullet and them spell critical casting a disintegrate as a swift action.

It should deal:

4d12+4xDex+20Enhancement first barrel crit + 15d6 empowered intensified Shocking Grasp crit + 24 Devastating Strike + 3d12 Greater Vital Strike + 1d12+Dex+5 second barrel hit + 216 maximised Distintegrate + 16 named bullet for a total of 420ish damage or just about enough to drop a CR20 red wyrm straight from the sky (well from 40ish feet in the sky, but still).

It would require the Greater Vital Strike chain, Devastating Strike, Intensify, Empower and Maximise Megamagic, Spell Focus (Transmutation), Greater Spell Focus (Transmutation), Spell Specialization (Disintegrate), Spell Perfection (Disintegrate), Spell Penetration, Greater Spell Penetration, Reach Spellstrike Arcana.

Does this work the way I think it does?
Is there some reliable way to ensure me rerolling 1s on the attack roll or enemies rerolling 20s on their save?
Would taking the Hexcrafter Magus archetype and Improved Natural Attack + Hex Strike + Conductive weapon work for delivering misfortune hex and if it works, how can I boost it's DC?

[Just a Mort]

I'm not sure how your caster levels are going to look like on both sides of your Gestalt.

As a Gunslinger, you don't qualify for EK - as you have no caster levels to add on that side. I don't know if you can use your arcane gun side to qualify for EK, since its on the other side of your gestalt. So you may not even get disintegrate from making your EK casting add to your Arcane Gun levels.

If you did Gunslinger/Eldritch Archer | Arcane Gun/Eldritch Knight, it might make more sense.

In that case, your shocking grasp would probably not land as you don't have full caster levels, the great wyrm has decent spell resistance. And you wouldn't qualify for Greater Vital Strike.

[Anger Nogar]

There are no two sides of gestalt (at least to my knowledge), you just take two levels in different classes at the same time. I just take one level in gunslinger and wizard each until level six at which point I start taking levels in magus and eldritch knight with the latter adding to my wizard casting.

Also I am not using my magus slots to cast shocking grasp against enemies with spell resistance, I cast it from my wizard slots (I don't think there is an issue with that since it is present on the magus spell list).

Of course I might be wrong... I have very little experience with the gestalt rules.

[Atarlost]

The gestalt rules forbid using hybrid PrCs. Eldritch Knight, since it existed when they were written, is specifically called out.

[Anger Nogar]

Balls... though it was only for dual casting classes. Oh, well...

[nate lange]

There's no official gestalt rules- it's a carry over of some optional rules from 3.x so it's always a good idea to run your ideas by the GM. Some will allow eldritch knight, some don't allow any prestige classes, some will make you track your 'sides' separately and make you use whichever 'side' is better across 16 levels instead of whichever is better at each individual level... the point is, there's enough variation that you should really find out exactly how the GM wants to run it before you work up a complicated build.

[SmiloDan]

Maybe a party member help with natural 1s and 20s? Like a witch or Luck domain cleric or some kind of oracle or Rage Prophet? Do some races have luck-like traits, like halflings or catfolk?

And definitely double check with your GM about what version of gestalt you are using.

And good job using gestalt to make a character that focuses on a single thing (without being a one-trick pony!). Often, gestalt builds try to be TOO versatile, and then get locked down when they try to decide what to do. For example, if you made an oradin//rogue/wizard/arcane trickster, you might freeze in combat when you have to decide if you should cast a divine spell or heal, cast an arcane spell, tank, smite, cast a Quickened spell, move into flanking so you can sneak attack, or 5 foot step and full attack, etc.