PFD, 3.5 gestault

[Fouredged Sword]

I had an idle thought.

What if, in a pathfinder gestalt setting, one side of the gestalt was 3.5.

Everything other than classes would be pathfinder unless there was no pathfinder version.

All 3.5 classes had to be taken on one side of the gestalt, and all pathfinder classes on the other.

So one could be a

Paladin (PF) // Wizard (3.5), but not a Paladin (3.5) // Wizard (3.5) or the reverse.

Where would this break and what should I look out for from an optimization and rule failure perspective?

[GoodbyeSoberDay]

Gestalt is insane, any way you put it. 3.5//PF, PF//PF, 3.5//3.5, 3.PF//3.PF, are all going to have the potential for serious shenanigans. You're going to have a lot of the same aspects in any of the above:

-Fractional BaB/saves are a good idea
-Theurge feats and classes are really powerful (hence the suggestion to ban)
-Double PrCing is really powerful (hence the suggestion to ban)
-"Passive"/"Defensive" classes pair well with "Active"/"Offensive" classes
-General optimization level is going to matter even more now than in regular D&D
-Limited-use action-granting abilities, like Factotum's cunning surge, White Raven Tactics, or Belt of Battle (MiC), or one of many Psionic powers, are even better when you have double the limited-use resources and hence are less likely to run out in a day.

As far as 3.5/PF combinations, just note that there are broken things on both sides of the aisle. When you combine the rulesets, you basically get most of the broken stuff. If your group is the type that exploits it, this may entail more work for you. That said, if your group tends to exploit crazy rules, I would not recommend gestalt at all. Also, if you have less rules-savvy gamers, I would at the very least point out which chassis is superior to avoid some power variance. For instance, PF sorcerer > 3.5 sorcerer.

Gestalt isn't a finished rule set, especially not for a combination of 3.5 and PF. There are going to be a lot of nitty-gritty questions on rules:
-If you choose PF's paladin or cleric chassis, can you use his "channel divinity" to fuel an ability that requires Turn Undead uses? Does undead turning even exist?
-[Ability] exists in PF and 3.5, but they're entirely different in everything but name (so not Power Attack, but Persistent Spell). Both, or just PF?
-When does favored class bonus come into effect?