Hey everyone!
I've been playing NWN1 online for about 7 years now. Started out with full Clerics only, then went to Sorc, then Wiz, then Druid, and now, believe it or not, I'm back to Cleric. I know what many of you are thinking---what a boring character! Well, after playing the other "standard" spellcaster classes, I have to say that the Cleric class seems to be by far the best all-around of the standard casters. The base hp of d8 is certainly decent, compared to the mages of d4.
I think there should be two types of cleric builds (both straight on all the way to level 40). The type you build depends on the module. In the most recent module I'm playing, there is no option to take the two different domains, so I had to simply pick one of the standard domain mixes (Elementalist, Generalist, Champion of Torm, etc.). The Elementalist or Battle Priest ones are probably the best, because with either of them you get stoneskin. However, in these types of "restricted" modules, a Cleric's offensive spellcasting ability is significantly decreased, as will be explained below. So...it's best to go "melee-based" with this type of Cleric. Focus on melee weapons and melee feats, do 18 WIS and 14 STR go begin with, add 1-2 WIS points later, and the rest should go to STR. This is because for Overwhelming Critical and Devastating Critical, the base STR needs to be 23 and 25, respectively. Once you get to that point, you will basically have a fighter/spellcaster in one class---how can you beat that package? The best offensive spells are 4th: Hammer of the Gods, 6th: Blade Barrier, and 9th (the best of all 9th level spells): Storm of Vengeance. Remember that you can pick the Metamagic Feats Empower Spell and Maximize Spell, to help overcome the crappy offensive spell selection for Clerics.
For either Cleric build, focus on the skills of Concentration, Spellcraft, Tumble, and Discipline, in that order. Spellcraft is important in getting Epic Spells, such as Epic Mage Armor, Hellball, and Epic Warding, all three of which should be taken as epic feats (if your AC is over 50, Epic Mage Armor may not help much). I tried the Dwarven Defender Prestige class with a Cleric, and was not impressed at all. It's basically just more HP, something you can easily obtain with any other character, by boosting your CON with various enhancements found in most modules.
For the other "spell-based" Cleric build, I would strongly recommend the Air and Magic Domains. With the Magic Domain, you get Melf's Acid Arrow and Stoneskin, both of which are very helpful. With the Air Domain, you get one of the most powerful and underrated spells of all: Call Lightning (as well as Chain Lightning later). Call Lightning is a humble 3rd level spell normally reserved for Druids. It's by far the most powerful 3rd level spell, and often more powerful than many higher-level spells, which means you should take the Metamagic Feats of Empower Spell and Maximize Spell for Call Lightning and other offensive spells. Call Lightning has a huge area of effect, and with about 34 WIZ, and level 25 Cleric, I've been able to do 350 HP of damage to many different kinds of monsters, often killing 10 at a time, with a simple, straight 3rd level spell. This is what I was referring to in the previous paragraph---the first type of Cleric build doesn't get the lightning spells, which REALLY help offensive spell capabilities. With this 2nd build, get Zen Archery for your missle weapon (crossbow or bow), point-blank shot, rapid reload if you choose a crossbow, weapon focus, etc. I'd forget about melee weapons---you are going to be a very powerful caster that can also shoot at your opponents. By level 26 you are really going to be kicking some butt. Don't forget to raise your Spellcraft skill high enough to take Hellball and Epic Warding.
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The Druid class has many drawbacks. It seems like a great class due to the polymorph abilities, but the problem is that if you have any enhancement to your WIS score (by rings, etc.), those extra spell slots disappear when you polymorph into a monster. This is a real pain, because losing even 1-2 spell slots for most of your spell levels kind of defeats the purpose of picking a spellcaster to begin with. Also, you can't use heal potions or spells while you are polymorphed, and don't even ask me how many times I've polymorphed, fought monsters until my hp are low, run away from the monsters, hitting "cancel polymorph", and getting a few seconds of lag, after which I'm dead. Not fun! Last but not least, the weapons that a druid can use absolutely suck, especially the missile weapons. I thought that the Druid may also be better than a Cleric because it had more offensive spells, but as you will read below, the Cleric can get around this problem in a couple different ways.
Sorcerers are fun, and it's nice to always be able to cast a spell that you don't have to memorize the night before. For example, if you are a Wizard, you may have one slot for Improved Invisibility. Once you attack something, that invisibility is gone, and you have to rest before it comes again. If you need it again after a battle, a Sorc can simply click on it again, as long as there are available spells for that level. This can be very handy. Also, a Sorc's number of spells, as mentioned in the NWN manual, accumulates faster than a Wiz, and also "peaks out" earlier, around levels 22-26, which means that you can add a prestige class for 10-20 levels without sacrificing much spellcasting ability. The prestige class I would recommend would be the Red Dragon Disciple, if only for the extra ability increases in Strength, Con, and Cha. The breath weapon is not very good at all, and plus by the time you get a decent weapon out of it, you are going to be doing a lot more spell damage anyway.
I would not recommend the Arcane Archer prestige class to mix with the mage classes. You get a +1 attack bonus/level, and with the AA class, you get one every two levels, in addition. So, it's 25% more of an attack bonus total, which is nice, but actually overrated in reality. A lot of monsters are hard to hit if you are simply a spellcaster with an AA class added on, so the extra attack bonus may not really help you hit them anyway. The imbue arrows with the spell Fireball (I assume level 5) is nice for a 2nd level AA, but it's really a base fireball spell from your bow. Interesting, and kinda fun, but on a practical level, it's not significant past (total class) level 20. It only causes an avg. of 15 HP damage. The rest of the AA class perks are not even worth mentioning, especially the mass arrows/number of monsters, since they cause only 5-10 hp damage/arrow. Pretty lame after taking several prestige levels.
For Wizards, I think that the Pale Master prestige class may be the way to go. The first time I tried it, I was disappointed because the paralyzing or death touch arm hardly ever worked (the high HD monsters you fight at higher levels have too high of a saving throw). However, it is nice to get extra HP for a mage (always need that), as well as extra spell slots every other Pale Master level. Also, summoning extra undead is nice, although most of these monsters are not really much more powerful than the standard summon monster I-IX spells. They will die too eventually, and die quickly against strong opponents. They are kind of like a free feat, like Mummy Dust, for example. I would not suggest doing melee with a Pale Master build, even though the manual hints at it. I mean, if you want to do melee, don't pick a mage class, no matter what prestige class you add on to it. Mages are for spellcasting, some missile activity, then running away. Any other action is grounds for dying quickly, unless you have Epic Warding. I've seen in the other forum, that people recommend either 26 WIZ / 14 Pale Master, or 10 WIZ / 30 Pale Master. Probably the first combo is better---I have yet to do either, but I always want to make sure I get good Epic Spells with the WIZ class---after all, what good is being a mage if you can't cast the best spells in NWN?