You're looking for this handbook, aptly titled: "Ways to Expand a Spell List".
With the requirements you stated above:
Magic Item Compendium - Runestaves - Item
- allows an arcane caster to expend a slot to cast the spell in the staff
Explorers Handbook - Drake Helm - Item
- Can attune spells to the helm; act as if they are on your known-spells list
Also, don't forget summons. Many summons can cast spell-like abilities, which makes your "spells known" a practice in "how well do you know your summon monster list?"
Furthermore, don't underestimate the leadership feat. A level 20 villain can have a level 18 cohort who specializes in arcane geometries and other nuanced spellcasting... and is a prepared spellcaster. If your main villain is the mailman and his "grand vizier" is an archivist or factotum/chameleon, you get a scary evil dude and his crazy-prepared henchman who gets all the work done. The henchman, himself, will have a psion as a cohort, and the psion will have a binder/anima mage as a cohort...
Evasion doesn't stack
Unless it specifically states otherwise (and some of them do), gaining duplicates of class abilities doesn't do anything special. You just get the ability to do... something you can already do.
For things with effects based on level, like Turn Undead and Wildshape, whether or not they 'stack' with each other to determine what effective level (EL) you use the ability at is complex thing that depends on FAQ answers and the specific sources of the ability and stuff. It's a whole nother answer worth of information.
Evasion does not stack. Uncanny Dodge, another rogue ability, has a specific caveat;
If a character already has uncanny dodge from a second class, the character automatically gains improved uncanny dodge instead, and the levels from the classes that grant uncanny dodge stack to determine the minimum rogue level required to flank the character.
So a common house rule for multiple sources of Evasion is to grant the character Improved Evasion.
If you have class that grants an actual Feat, like Ranger grants the Track feat, and you already have that feat, unless the entry says 'if you already have the feat, you may pick another' or something similar, you just get.. nothing.
A common houserule is that you get to pick a different feat in those circumstances.
Even with that houserule, though, gestalt's basic rule is that if you get something from both sides of the gestalt, it overlaps, it does not stack. This is applied to BAB and saving throws explicitly, but a common houserule applies it to everything - so you can't dual-progress Sneak Attack by playing a Sneak Attack Fighter//Rogue, and you can't dual-progress your Wizard casting by playing a Wizard//Something/Loremaster.
So basically, under the rules, and under the common gestalt houserules, that character gets nothing special for getting evasion twice. Equally though, many tables grant Improved Evasion when you get Evasion twice, so you could go with that.
By RAW, you get nothing. By houserules, you could get nothing, or you could get improved evasion, or the GM might feel nice and grant a feat or a bonus to reflex saves or something. It's up to the GM, though, there is no explicit rules granting you anything at all for getting Evasion twice.
However, there is stuff that trades Evasion away
While you can't get Evasion twice by RAW, you can trade Evasion away once and still receive Evasion, such as by an Alternate Class Feature, or a Level Substitution. I'll list some of the better ones here.
- Spell Reflection [Complete Mage] - Trade evasion for the ability to reflect targeted spells that miss you.
- Dungeon Specialist [PHB II] - Trade evasion for a climb speed.
- Mettle of Mountains (Goliath Rogue Substitution Level) [Races of Stone] - Lose Evasion, gain Mettle (and bonus to Fort saves).
Best Answer
The rules don’t really say; gestalt is a variant that’s pretty well fleshed-out, but it’s even less comprehensive than the usual rules.
Generally speaking, there’s no reason it can’t work. Particularly for a non-player character, where LA doesn’t come into play, you can just gestalt it with Monstrous Humanoid RHD. It will be fairly effective without being as devastating as having both all those RHD and all those class levels (i.e. many more total HD). It’s a quite appropriate way to power up a monster without making a lot of math wonky by inflating coincidental numbers.
But the rules don’t actually suggest or recommend this approach (or suggest or recommend against it, for that matter).
Challenge Rating
As for CR, that’s a nearly-impossible question to answer. I’m reasonably confident that I could find CR 3-4 monsters that could keep up with this guy (allips and That Damn Crab come to mind), and also reasonably confident that I could find CR 10-12 monsters that he could handle. Meanwhile, 6th-level parties could potentially founder on those CR 3-4 monsters, or kill even things CR’d higher than that 10-12 range. CR is, effectively, useless, because there’s no standardization.
For this case, are we claiming that a Fighter 6 is a CR 6 encounter for this party? Most parties I’ve been in would make short work of a Fighter 6 even at levels well below that (quick, four Will saves, fail any one and you’re out of the fight!), but nominally it’s a 6th-level character. For the sake of giving some answer, I’ll assume it is.
So what does being an ogre add here? Large size, which is awesome, +5 natural armor, which, fine, OK, and... that’s about it. If you use the elite array, some really solid ability scores, but lacking the Intelligence to take Combat Expertise and therefore Improved Trip (unless he dips Wolf Totem Barbarian 2, which would be awesome for him). With Large size and no trip, I’d want to go with Dungeoncrasher from Dungeonscape, grabbing Power Attack, Improved Bull Rush, Knockback (Races of Stone), and Shocktrooper (Complete Warrior).
He now can potentially do huge damage if he shoves someone into a wall, and he gets a free bull rush on each attack. Easily looking at around 70 damage on a charge or regular bull rush since you can safely Power Attack for full in those cases, and 60 damage on a regular attack (with the possibility of an iterative), assuming that he can’t reliably hit while Power Attacking for full. But that damage is contingent on slamming things into walls. Aside from bull rushes, he has no ability to control the battlefield, which means a smart group can deny him the ability to land that damage; typical attacks are going to be more like 20 damage, up to about 35 if Power Attacking becomes an option (e.g. on a charge).
Since landing both iteratives is probably unlikely, and a single dungeoncrash hit probably won’t kill in one, that could make the fight an interesting tactical encounter in the level 6-8 range. Or it could be brutal because there aren’t good options for avoiding the dungeoncrashing, the party isn’t prepared to protect squishier assets, and so on. Or it could be a cakewalk because the party immobilizes him well away from any walls and just destroys him.
Ultimately, I would CR this encounter based on how many times I expect a character have to weather a dungeoncrash hit, and look for HP values based on that. For my parties, I’d expect them not to let him do it twice, so I’d want them to survive the first hit but die if they were dumb enough to let him do it twice. You might want to give a little more leverage based on how quickly you think they can evac whoever took the hit, and how capable they are of preventing a second. For two-hit kill, probably around CR 6-8 like I said. For a three-hit kill, probably around CR 10, though I’d boost his health and saves for that. His damage is too high to allow more hits than that at levels where he could even conceivably be a threat.
If you don’t go with Dungeoncrasher, his damage goes down dramatically, and it eliminates any real hope of getting a particularly tactical encounter out of this. Then it just becomes a calculus of how many hits you expect the party to have to take in order to put him down, and CRing him based on that. Hopefully they haven’t got any clever battlefield controllers.
For players: LA
For the record: when a player in a gestalt game wants such a character, the question of LA has to be addressed. This is somewhat awkward. But in my experience, and I’ve played in many such games, simply putting the LA on “one side” of the gestalt works well (though it will be inconsistent with NPC gestalt characters built as above), since most monsters are over-LA’d and the gestalt devalues the effect. In most cases, it’s still underpowered, though of course exceptions abound.