Are there any size increases that don’t reduce Dexterity?

Question

I have a character who is interested in increasing their size, but relies on Dexterity and so does not want to take penalties to that in the process. Are there any options for doing so? Shapechanging is generally out, because I need to keep the attributes of my own form.

The character in question has 10 levels of the ninja class from Complete Adventurer, using the water ninja variant class features from Dragon vol. 354. Since 10 levels are dedicated to this class, this limits other options. Righteous might is the one option I’m aware of with no Dexterity penalty, but a 10th-level ninja/9th-level cleric seems like a painful combination to me, and 19th level is a long way to wait for just one size increase.

The other option is mountain rage, which also has no penalty. However, since you have to be a goliath to get it, and they do have a penalty to Dexterity, that doesn’t help very much. Arguably, ferocity could counteract that, and there is technically the option of the stoneblessed prestige class from Races of Stone to count as a goliath, but stoneblessed is three levels of nearly-nothing for the privilege, and while ferocity might be good if I’m investing in it I’d want to keep all of that bonus.

Finally, since for a moment I thought it might, let me note that half-minotaur doesn’t work here: while it doesn’t apply a Dexterity penalty in its Abilities rules, the Size and Type rules tell you to “See Table 4–2: Changes to Statistics by Size in the Monster Manual for changes to the base creature when it gains a size category. The changes in this template are in addition to the changes outlined there.” Table 4–2 would be this one, and it does apply a Dexterity penalty for almost-all size increases (unless I’m already Huge, which is not a size I expect to reach ever, and certainly not at 1st level). Most player-available size changes don’t use those rules (those were initially just for size changes when advancing monsters), which gives us some hope, but half-minotaur specifically invokes them.

Effects that grant Strength bonuses are acceptable, but most Strength bonuses are costly, so expensive options whose value is supposed to come from a Strength bonus are not great. What I’d really, really like to see is some option that allows me to swap the Strength bonus to Dexterity, or barring that, something that just says “You don’t take Dexterity penalties for increasing your size,” which would enable me to seek any size bonus I want here.

Any 3.5e content (including 3.5e-legal 3.0e content) that is published by Wizards of the Coast or in Dragon or Dungeon magazine, as well as Pathfinder content produced by Paizo, is acceptable, with the exceptions of epic and/or mythic material, and anything with a level adjustment greater than +1 (and even a +1 is something I’d really like to avoid). Please note sources, and also note if there is a conflict between 3.5e and Pathfinder on a given option—for instance, Pathfinder-style shapechanging might work, but that conflicts with 3.5e. We’re generally favoring 3.5e here, but a case can be made for specific Pathfinder items ported.

Answer 1

Righteous Might

While it's true that a Ninja 10/Cleric 9 is a somewhat dubious build, there are a few other options to access the spell. As maligned as it is, making mid-level adjustments to a build is what the prestige class Ur-Priest was designed for, and entering it at level 11 is hardly overpowered. In fact, even setting aside the RP requirements, it's probably underwhelming. If you have ranks in Use Magic Device (not a terrible idea, though it's cross-classed for Ninjas), you could get a wand of righteous might; it's a 4th level Runescarred Berserker spell, so Artificers and Warlocks can create such a wand. Or Runescarred Berserkers, I suppose. Alternatively, any Cleric with Sanctum Spell can stick a 5th level spell into a wand as long as it's crafted outside the Cleric's sanctum, though some DMs might frown on this probably-unintended use of Sanctum Spell.

Some other spells

• The spell alter self lets you keep your ability scores while letting you shift into a form "within one size category of your normal size." This means it doesn't stack well, but if you're just interested in being large, it's a 2nd level core spell and thus should be accessible in some form. You've said you're uninterested in spells "that start replacing things about the character entirely," so it's worth pointing out that alter self will make you lose breath weapons, gaze attacks, and probably natural armor, weapons, and movement (the spell technically only says that you acquire such things from your new form, not that you lose those you had in your old form; good luck arguing that to a DM, though).

  Though getting big is a fair use of the spell (enlarge person is 1st level), it should be noted that alter self is very, very powerful if one goes diving through books for optimal forms. Veteran DMs may ban it, or otherwise restrict its use; I would argue that simply increasing in size is a fair use of the spell, though, and it's worth asking your DM even if alter self is normally banned at your table.

• Fiendform (Spell Compendium), a spell based on alter self, is also worth considering; you "take the form of any fiendish creature, demon, or devil that can be summoned by a summon monster I, II, III, or IV spell (MM 287)[sic], regardless of size." It's actually referring to the Player's Handbook, not the Monster Manual; there are several huge forms on the list, though fiendform is a 5th level spell, so access is no less difficult than access to righteous might, and you're more likely to lose things you care about (like arms, if you chose the huge fiendish viper, for example).

• The spell infernal transformation (Spell Compendium) increases your size to large and gives a +4 profane bonus to strength and constitution, along with a bunch of devilly traits. As a 7th level cleric spell, you'd almost certainly gain access to righteous might first, but if you do pursue cleric casting it might be worth having this one in your back pocket.

• The spell spider curse (Spell Compendium) makes you large (though with 5' reach only) and gives +4 untyped bonus to strength, dexterity, and consitution. You basically become a drider, and it lasts 24 hours/level. The downside is that it puts you under the control (as per dominate person) of the caster, and said caster is probably a crazy drow, because this is the Spider domain's 6th level spell. But if you find a drow cleric you trust, this spell is pretty sweet.

Lycanthropy

• Become a werebear or weretiger: Unlike most shapeshifting in 3.5, lycanthropy keeps one's original physical stats, simply modifying them. The two large forms presented in the Monster Manual are the werebear and weretiger, both of which actually increase dexterity when shifting into animal or hybrid forms. They also give +16 or +12 strength, respectively, which seems reasonable. Now, normally becoming a werebeast is ruinous to a character's advancement; both werebears and weretigers get 6 levels of animal hit dice to go with their +2 level adjustment, which effectively means you never get to level up again. If you make friends with a vampire, though, the vampire can slurp away your six most recently gained levels (the animal ones), leaving you with just +2 LA to deal with. If your DM doesn't allow LA buyoff (an optional rule from Unearthed Arcana), this is still probably a poor choice. If they do, though, at level 10 you can spend 16,000 XP to buyoff your level adjustment (debatably you need to be level 6 to buyoff the first LA and 9 to buyoff the second, but you have a vampire friend and hopefully access to restoration, so that's doable), which is probably worth large size, +16 strength, +2 dexterity, and +6 constitution. (As a side note, the vampire isn't strictly necessary, here; a +1 unholy arrow will do the trick for 360 gp. But vampires and lycanthropes go together like peanut butter and jelly.)

• Become a Pathfinder werebear or weretiger: Easier, probably, though much weaker. PF lycanthropes only get +4 STR, +2 CON, and -2 CHA, but they also don't add 6 animal HD or any level adjustment. You say you're generally favoring 3.5, but even so this might be more palatable than cheesing level loss with a friendly vampire.

Rely on an NPC

• Ask a big Egoist to manifest fusion. A fused creature has the best physical stats of either of its constituents, so presumably it'll use your dexterity while using the manifester's size. You'll need some way to convince this hypothetical large Egoist (who's at least level 15) to relinquish control to you, however, since by default whoever manifests fusion gets to be in charge. I would hesitate to call this a practicable option, but hey, maybe your Ninja is in a party with an Egoist. That would be fortuitous.
• Get a Void Disciple (Complete Divine) of at least 10th level (ECL 17, unfortunately) to use Void Release on you after you get big and strong. This will let you use your strength in place of your dexterity for a few rounds. Then your DM will read the rest of the Void Disciple's class features and ban it from the campaign—its abilities are notoriously vaguely written. Void Release, however, is fairly cut and dry, and pretty much directly "allows [you] to swap the Strength bonus to Dexterity."
• Get a Spellsword to stab you with righteous might. The Spellsword's (Complete Warrior) Channel Spell ability is extraordinarily powerful, letting them completely ignore casting time and targeting restrictions on their spells. Assuming one had access to righteous might (the Complete Divine feat Arcane Disciple is probably the easiest way, though there are many), they could poke you and affect you with righteous might. They could actually probably poke you and affect you with enlarge weapon or something, too. But be careful, because you probably don't get a Spellcraft check to determine what spell they just channeled into their sword, and geas doesn't allow a save.

Of these, I'd say alter self is the easiest, while Ur-Priest and becoming a werebear are both totally doable but might require fundamental changes to your character that could dilute its identity.

A wand of righteous might is also totally reasonable, but it would require some retraining to get ranks in Use Magic Device and probably a way to add it as a class skill, like the Apprentice (Spellcaster) feat from Dungeon Master's Guide II.

None of the "find an NPC" options are practical if you're looking for an actual NPC, but it might be much more doable to team up with a fellow PC to pull off some combos.

Answer 2

I recently just did a chart of all the polymorph spells I could find (largely based off all the druid wildshape spells) for pathfinder. Roughly 90 different spells (counting size and element as individual spells).

The Elemental body Air and fire forms are the only one I know of which going from medium to large or bigger increases the dex bonus, neutral (no change) are not included.

Since there are also ones that increase size but dont hurt dex, theres plantshape 2 for large. Form of the (normal, alien, exotic) dragon spells. Frightful aspect.