Is a feat that allows one more swift/immediate action per round balanced?

Question

The epic SRD has this feat:

Multispell [Epic]

Prerequisites: Quicken Spell, ability to cast 9th-level arcane or divine spells.

Benefit: You may cast one additional quickened spell in a round.

Special: You can gain this feat multiple times. Its effects stack.

Now, the combat guys are complaining they want a similar feat for extra swift/immmediate actions in a round.

So I am thinking of homebrewing this:

Multiswift [Epic, fighter]

Prerequisites: BAB 18, Combat Reflexes

Benefit: You can perform one extra swift or immediate action in a round. You cannot cast quickened spells in the round you take this extra action.

Special: You can gain this feat multiple times. Its effects stack.

I've tried to leave the BAB requirement not 20 to allow some Gish multiclass character to take them.

Are the prerequisites OK? Is it balanced? Is there any potential obvious exploit for this that I've not seen?

Answer 1

So, you're using the epic rules. At those levels, nothing will balance non-spellcasters with spellcasters, and trying to do this is an exercise in futility. That said, the creation of a parallel feat makes some sense and should be doable given our example feat, provided we make the assumption 'one extra quickened spell per round' is balanced and that 'one extra swift-action-y nonspellcaster thing' is of equal value.

When we do so, we see some discrepancies between the Multispell feat and your own.

Prerequisites:

Multispell requires Quicken Spell, which is necessary for its use and furthermore necessary for high-level D&D play between getting 9th level spells and getting Epic Spellcasting. It also requires 9th level spellcasting in a single class, which the game generally treats as equivalent to 'level 17'.

Your feat requires Combat Reflexes, which I happen to like as a feat, but isn't actually central to what your feat does, nor necessarily present in your melee's builds. There's no way for them to definitely be meaningfully contributing at these levels, so we have no idea what feats they've taken. Even if the only classes are melee characters, there's a bunch of different builds that rely on charge+pounce or Tome of Battle classes or whatever, and so don't need Combat Reflexes and are probably too feat-starved to take it.

There are feats that all mundane characters generally have, but the thing is no one takes them willingly cause they are awful and you get them for free. I'm talking about Martial Weapon Proficiency and Simple Weapon Proficiency. Obviously, neither of these is a particularly good feat as a gate against spellcasters that doesn't impact martials, but requiring proficiency in all martial weapons at least stops most full casters and allows most martial classes. Proficiency with all simple weapons lets in the rogue and expert at the cost of also letting in the Cleric (although they could already get in without too much effort if they felt like it) and Adept. There's no way for proficiencies to let in commoners without them spending resources on it or Wizards, Druids, and Sorcerers also being allowed.

@HeyICanChan has provided a pretty elegant solution in requiring two non-simple weapon proficiencies, which blocks all the mentioned full casters barring extra proficiencies from race while letting in both the monk and the rogue. That's probably your best option for a simpleish yet moderately effective anti-caster prerequisite.

Rather than requiring a feat and dealing with the lack of equivalencies detailed above, you might want to just require 'ability usable as a swift action', mimicking only the need for Quicken Spell to use Multispell rather than its status as a feat.

Your feat requires BAB +18. That should really be BAB+17, since it's paralleling 9th level casting. If you want it to be accessible to partial advancement classes like the rogue, bard, and monk or what have you, it should be BAB+12. Note that clerics and druids also get the +12 at 17th level advancement.

Benefit

Blocking just Quicken Spells and for the whole round is kinda weird. Consider instead just banning all spellcasting and spell-like abilities with the extra action it grants. That'd be simpler, and not really any more broken, since we're already in Epic play. The biggest problem I have with your version there is that blanket banning something for the round and involving immediate actions makes it matter what actual initiative count we're on, rather than just order: if I cast a quickened spell on my turn on count 7, I can't take an extra immediate action on count 22 (since that's the same round), but I can on count 3 of the next round (since that's a different round) even though it's still before my next turn, and doing so bans quickened actions in my next turn rather than this one (except then the language is weird).

Another problem with the current wording is that it either allows players to use magic items mimicking quickened spells (which probably isn't what you want) or allows players to use scrolls to enter some prestige classes early, bypassing 'ability to cast X level spells' prerequisites. The latter isn't really a huge problem (I play that way normally), but it might be an issue for you if you aren't used to it.

Special

Yeah, that's the same. It's fine.

In Conclusion

The feat is roughly similar, but could use a little polishing on the prerequisites and the restriction mechanism in the benefit could be reworked for ease of play. It can't ever be actually balanced in the larger sense of the game, but it can be made to thematically and mechanically mirror the multispell feat, but for abilities that aren't spells (and spells with native casting times of 1 swift or immediate action).

Answer 2

No, it isn’t really.

Swift and immediate actions are designed around being only once per round. The only source of extra swift actions in the entire game is ruby knight vindicator, and that class feature alone makes it one of the best classes in the game—and gives it a starring role in a number of theoretical optimization tricks. Something as simple as a feat for just an extra swift action per round, with no other costs or caveats, is a feat that almost every character will want to take. In fact, it’s good enough to justify going out and finding more uses for your swift actions, since the feat will enable you to use them.

But it doesn’t really matter anyway—Epic isn’t balanced to begin with.

D&D 3.5e starts falling apart in the teens, and is almost impossible to hold together as 8th-level and then 9th-level spells come into play. At 21st, the impossibly broken Epic Spellcasting feat becomes available, destroying any illusion of balance that the game had left. If you are playing Epic, then by definition balance is very low on your list of concerns. Balance in Epic play is simply not possible.

Answer 3

As written, Multiswift encourages the use of magic items

Here's the thing: The Dungeon Master's Guide on Spell Trigger says, "Activating a spell trigger item is a standard action and does not provoke attacks of opportunity" (213). However, the Rules Compendium on Spell Trigger says, "Activating a spell trigger item takes the same amount of time as the casting time of the spell that the item stores…" (85).

This makes the feat Multiswift an outstanding choice for, for example, a creature that has sufficient ranks in the skill Use Magic Device and a custom magical staff that's been created with spells that have been modified by the feat Quicken Spell (as per DMG 282–3 and expensive but well within the budget of a typical epic adventurer). Of course, the feat will still be useful even without the skill Use Magic Device: many largely mundane adventurers will nonetheless have a spell list or two they can use to activate spell-trigger magic items—assassins, paladins, and rangers all get a pretty big spell lists, for instance—, and, at epic levels, new magic items should be fairly common, and creating new magic items that can be activated as a swift action should be within an epic magic item's creator's power.

That is, the feat Multiswift will see epic yet otherwise largely mundane combatants snapping their fingers to bring forth their magic staffs, buffing themselves or blazing away at enemies with their magic staffs, snapping their fingers again to disappear those staffs, then go about charging their enemies for some of the ol' snicker-snack just like they always have.

While the feat Multiswift does successfully add another limited range of options to the mundane combatant's abilities, the best of those new options are—like pretty much always—just more expensive and ultimately inferior versions of the options opened up by the similar feat for casters, Multispell (Epic Level Handbook 63).

However, if activating magic items is the intended use of the swift action granted by the feat Multiswift—and it very well could be, as that's one way to struggle (quite vainly, really) to bridge the enormous gulf between, for example, epic fighters and epic wizards—, then ignore the next section, and the feat's doing what it should.¹

Consider a less sweeping alternative

Having run two campaigns in the past 5 years involving high-powered PCs going from level 1 to level 20 and stopping there, this DM thinks that spending a feat to take every turn an extra swift action is far too inexpensive. Even the feat Multispell feat doesn't go that far, granting, essentially, a swift action that can only be used for casting a spell—a broad and terrifying mandate to be sure, but substantially different from a feat that allows taking a swift action to do anything but cast a spell, like, for example, employ a quickened spell-like ability, use an appropriate Tome of Battle boost, or activate one of those aforementioned magic items.

I think a closer equivalent to a mundane version of the feat Multispell would be a homebrew feat looking something like this completely unplaytested feat:

So Fast

[Epic] (Fighter bonus feat)

Prerequisite: Base attack bonus +11, proficiency with either two martial weapons, two exotic weapons, or one martial weapon and one exotic weapon.²
Benefit: Once per turn you can take a free action to, at any point during this turn, either take a move action that cannot be used for a normal move or make a standard attack at your full base attack bonus.
Special: You can take this feat multiple times, allowing the feat to be used multiple times per turn. For example, Regdar has the So Fast feat three times. On his turn, Regdar takes a free action to activate the first feat's benefit to make a standard attack. Then he takes a second free action to activate the second feat's benefit to sheathe Dark Edgerazor X, his totally 90s artifact longsword. Then he takes a third free action to activate the third feat's benefit, retrieving from his belt pouch a potion of resurgence. Regdar, despite having done all this, essentially has still his whole turn's worth of normal actions remaining, enabling him—on what is still the same turn—to move 20 ft., drink the potion of resurgence, and activate the benefit of the feat Law Devotion. Regdar's turn is almost as long as Mialee's!

It's this DM's opinion that for the largely mundane folks who plan to spend their combat time primarily hitting monsters with fists, swords, arrows, or whatever that the equivalent to casting more swift-action spells during a turn is not getting more swift actions with which to do whatever they want except cast spells, but, instead, getting more actions to perform the mundane tasks that they wish they always had more time to do yet don't, like stabbing an extra monster, sheathing an artifact longsword, or retrieving a stored item.

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¹ I totally agree with this answer that it's pretty much impossible keep epic level play balanced—casters really are just that good—, but kudos for considering the martial combatants' concerns.
² Thanks to this answer for its excellent examination of the original Multiswift feat's prerequisite. Hewing to those recommendations, this feat's prerequisite isn't met automatically by the typical human epic cleric, druid, wizard, or sorcerer yet is met automatically by any other core rules standard class; unfortunately, some nonhuman full casters will be able to meet them, too.