Ways to improve a Warlock's counterspelling capabilities

Question

How do I make counterspelling more efficient for a 3.5 Warlock? I've looked over a few caster builds for counterspelling; however not much seems useful/useable for a Warlock.

We are jumping into the game at level 12. There is no multiclass XP penalty; however, there is a 3 class cap imposed on Multiclassing. Also there will more than likely be no LA buyoff; therefore races and templates with even just a +1 LA would be a tough hit. Most published material is okay (including third party, 3.0, Pathfinder, Dragon Mag, etc). Homebrew would even be okay with the DM, but I would prefer to stay away from homebrew personally.

I am going a full Charisma build focusing on social skills and battlefield control. I also plan on taking a 1 lvl dip in the Mindbender PrC to get telepathy and Mindsight access to help us get the drop on most opponents before the battle even begins.

I'll be taking one of the dispelling lesser invocations (more than likely Voracious Dispelling). Having an at will Dispel Magic is great, but I am not sure how to maximize the success chance -- it has a cap of +10 to add to the roll (later on +20 the Caster's Lament invocation). I want to make sure my CL is at least as high as the cap.

Is there any other way to improve the success rate beyond that? Is there anything that would let me take a 10 on a dispel check, or a +X bonus on dispel checks?

It seems like the only metamagic imitating feat that has any real effect on the dispelling invocations would be Quicken SLA; however casting them as a swift or free action 3 times/day doesn't seem worth the feat to me.

The only real bonus that I have found for a Warlock to take for counterspelling (besides just having a plethora of scrolls on hand) is to dip in Cleric or Ur-Priest, take Practiced Spellcaster, and then take Divine Defiance. This grants a way to counterspell as an immediate action during my opponent's turn, to try to prevent anything that would be an instantaneous effect, especially to counter an opponent's Dispel Magic spell.

The only problem with the Divine Defiant route is, that without going an Eldritch Disciple build, that's a pretty big hit to my Warlock CL. And while it may be easy enough to raise my effective CL, any hit that slows my Invocations Known progression is HUGE. If there is another route to gain immediate action counterspelling that would be great.

If push comes to shove, I can homebrew a feat or two (something like "Instantaneous Spell-like ability" that improves Quicken SLA to an immediate action), but I only want to use that as a last resort. Another option for this particular situation might be just to convince my DM to let my casting go off of the Pathfinder Spell Duel rules.

I just found a Pathfinder feat called Dispel Mastery which I will take.

TL:DR-

1. How to get bonuses to Dispel Magic and Greater Dispel Magic?

2. How to use my dispelling invocations as an immediate action?

3. Besides carrying level 9 scrolls from all 8 schools and taking Improved Counterspell, what are other ways for my Warlock to counterspell effectively?

4. Is there a way to cast scrolls as an immediate action(Such as a feat that would let you do it on scrolls that were made quickened)?

   -Just about any published material is okay.
   -Homebrew will only be considered as a last resort option.
   -Races/Templates are fine, but no LA buyoff
   -3 Class max if multiclassing.

Answer 1

A single-level dip in cleric can get you three things: the Inquisition domain with its +4 to dispel checks, Turn Undead that can power Divine Defiance, and the ability to activate a prayer bead of karma for a straight +4 bonus to CL.

Ur-priest does get you the last two things, but it’s difficult to enter and you need two levels instead of just one to get Rebuke Undead from it.

Anyway, Divine Defiance is a feat in Fiendish Codex II: Tyrants of the Nine Hells, and it lets you burn a Turn Undead usage to attempt a counterspell as an immediate action. Obviously valuable.

In general, the cloistered cleric variant is a great 1st level to take for a lot of people: you get 4×(6+Int) skills, much better than you would as a warlock, you get all of the above, another domain, Knowledge Devotion from Complete Champion, and you get identify as a 1st-level divine spell, i.e. you don’t need the arcane material component for it. The Undeath domain can get you Extra Turning if you want it, or you can use the other domain to get all manner of excellent things. Check out the Dipping Cleric Handbook for more ideas.

Divine Defiance requires “divine caster level 3rd,” which warlock doesn’t qualify for. The solution to that is Practiced Spellcaster (cleric) from Complete Mage; that will get your cleric caster level (but not any other aspect of cleric spellcasting) up to 5th to meet the requirement. You will also most likely want Practiced Spellcaster (warlock) to get back the CL lost when dipping cleric, as that would otherwise hurt your dispel checks.

The eldritch disciple prestige class from Complete Mage could progress your cleric spellcasting along with your warlock invocations, but it’s not that great and it would require you to take another two levels of cleric to get the 2nd-level divine spells it requires. Not worth it. Shenanigans can get you in without those levels of cleric, and that might be worth it, but if you want to go that route I recommend just asking your DM to adjust the class’s requirements to begin with, rather than get into shenanigans. For example, eldritch disciple expects a Cleric 3/Warlock 1 entry, and then at 1st level gives you invocations only (so you are effectively a Cleric 3/Warlock 2 at 5th level) and from then on progresses both. Maybe your DM would be willing to flip it, allowing you to enter as a Cleric 1/Warlock 3 and then progressing spells only at 1st (so you are effectively Cleric 2/Warlock 3).

The other prestige class worth mentioning for any warlock is chameleon from Races of Destiny. The second-level bonus feat can be changed every day, which means it can be any invocation you need that day (by making it Extra Invocation), or if you get far enough, an Item Creation feat to go with your Imbue Item class feature. This makes Cloistered Cleric 1/Warlock 9/Chameleon 2 a pretty strong build for you, and when you hit Cleric 1/Warlock 12/Chameleon 2 at 15th, you’ll be exceptionally versatile.

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I will mention, however, that I have done a counterspelling warlock quite similar to the one I describe above, and while it works more or less, it’s pretty boring. If you are really interested in a high-power spin on the idea of ruining other casters’ day, what you really want is a Black Tactica build: use the war weaver prestige class to buff all of your allies as a move action at the start of combat, and then spend your actions in combat readying to target anyone who starts casting a spell. You don’t ready a counterspell, however: you ready the most reliable single-target nuke you have. In addition to hitting the spelcaster hard, which is painful, this also forces a Concentration check with DC 10 + the damage dealt. It’s trivial to pump the damage well beyond what anyone can hope to hit with the skill check, which means they will lose the spell.

This is a very high-power build that may actually make your game less fun, as your enemies start using similar tactics and combat becomes something of a deadlock, everyone readying nukes against the others, and whoever dares to move first still not getting anything done.

Answer 2

As far as buffing your dispel checks, these might help:

Elven Spell Lore Feat (PHB2): +2 on caster level checks when you cast dispel magic/greater dispel magic. Also other stuff not related to dispel magic. Feat requires you to be an elf of have high (17) int as well as having 12 ranks in knowledge arcana. Although your DM might be willing to change it to "(Insert your race here) spell lore" to make the feat a bit easier for you to take.

Soultouched Spell Casting Feat (Magic of Incarnum): Invest essentia for an insight bonus on dispel checks and checks to overcome spell resistance. Taking the feat also gives you one point of essentia to invest. Requires 13 Con.

Edit: Also, maybe look into Dampen spell feat, also found in PHB2. While strictly speaking its not counterspelling, and I'm not sure wording wise if you can expend spells from items to power the feat, it grants you the ability to, well, dampen enemy's spells as an immediate action if you can identify them. Might need some more doing to get this one to work, or maybe a flexible DM, but I think it might thematically fit your character very well and gives you the immediate action you are looking for without readying an action, even if it isn't a full counter of a spell.