Oh my, I've been loving me some Dungeons of Dredmor. I regularly visit the Wiki, which is a great reference guide for skills points & crafting recipes. But I haven't found anything like a real strategy article, so I'm attempting to correct that oversight.
In this first part of my guide, I'll be going over the core mechanics of the game, primary archetypes, stats, and general guidelines for building a character. In the second part and the third part, I'll provide a detailed analysis of each skill tree's merits.
Update: I've added a fourth part, detailing some character skill builds.
Update 2: I originally wrote this guide for version 1.0.3. Now that the game is in 1.0.10 and two expansions have come I thought it was time for an update! I've tried to leave my original text in place where possible, but a significant number of systems have changed..
The six primary stats in Dredmor are: Burliness, Sagacity, Nimbleness, Caddishness, Savvy, Stubborness. These each drive the value of some number of secondary stats, including health and mana values. Like most of the words in Dredmor, their names are 50% informative and 50% humorous. So let's look past the names and make sense of what these stats mean.
The core mechanic in Dredmor is that every stat, action, and skill is associated with either a Warrior, Wizard, or Rogue. Every skill you gain is associated with one of these three archetypes. Each skill point grants three primary stat points, as laid out below:
Warrior: +1 Burliness, +1 Caddishness, +1 Stubborness.
Wizard: +1 Sagacity, +1 Savvy, +1 Stubborness.
Rogue: +1 Nimbleness, +1 Caddishness, +1 Savvy.
Burliness, Sagacity, and Nimbleness (Red, Blue, Yellow) are the exclusive purview of Warriors, Wizards, and Rogues respectively. Caddishness is shared by Warriors and Rogues (Red and Yellow), and is colored Orange. Savvy is shared by Wizards and Rogues (Blue and Yellow), and is colored Green. Stubborness is shared by Warriors and Wizards (Red and Blue), and is colored Purple.
So we can see that, although the names are written to obfuscate, the color coding is here to help us.
Each time you level-up (by selecting a new skill) you gain +1 to all six base attributes and +1 to the three attributes associated with the archetype of your skill. If you grab a Warrior skill, you get +2 Burliness, +1 Sagacity, +1 Nimbleness, +2 Caddishness, +1 Savvy, +2 Stubborness. It is important to note that your rate of increase doubles in your primary stats - so while all of your secondary stats will increase as your gain in levels, secondary stats associated with your archetype will increase at double the base rate.
Your seven initial skills follow this same pattern - so it becomes trivial to calculate your stats at any level, for any given combination of skills. If you want to be a nimble character who dodges attacks, selecting "Dodge" as a skill choice will, in general, be less effective than simply picking all Rogue-archetype skills, which will grow your dodge attribute at 2x the base rate for the entire game. If you want to be a heavy-hitting warrior, simply taking all Warrior-archetype skills will do more for your damage and block rate than anything else you can do.
Your Life (HP) is calculated as 5 + Burliness + Caddishness. This means Warriors gain 4 Life per level, Rogues gain 3, and Wizards gain 2.
Your Mana is calculated as 5 + Sagacity*2. Wizards gain 4 Mana each level, everyone else gains 2.
Critical Chance (extra damage for attacks) is Caddishness / 2. Haywire Chance (extra damage for magical attacks) is Savvy / 2.
Counter Chance (hit an enemy back when they hit you) is (Nimbleness + Caddishness) / 6. Rogues get + 0.66 per level, Warriors get + 0.5, and Wizards get + 0.33.
Block is (Burliness + Stubborness) / 6. Warriors get +0.66 per level, Wizards get +0.5 per level, and Rogues get +0.33.
Sneakiness is (Nimbleness + Savvy)*3 / 4.
Magic Power is simply Sagacity / 2.
Magic Resistance is simply Stubborness / 2
Dodge Chance is Nimbleness / 2. Enemy Dodge Reduction is Nimbleness / 3.
The biggest takeaway from this is the fact that Wizard skills, and the stats they drive, are totally uninvolved in anything except casting spells. If you don't plan to cast spells, you don't want or need a single Wizard skill! Conversely, Warrior and Rogue skills have some excellent synergy to them - trade-offs between block, accuracy, critical damage, dodge are very interesting, and lead to lots of viable character types.
Magic Power is calculated as half your Sagacity. It influences Wizard characters a great deal, and it has a few other odd effects which are worth talking about explicitly. First, Magic Power increases the damage of every spell in the game. It also reduces the cost (in mana) of every spell in the game. So clearly, if you want to be a wizard you need a very high Magic Power!
Update for v1.0.10! Spell costs are now reduced as a function of Savvy, not Magic Power. This means that Rogues get very low spell costs over time, just like wizards. It also means that + Magic Power gear doesn't reduce your spell costs. Magic Power is still just as important to wizards, but now it's worthwhile to try to increase your Savvy skill as well.
On the other hand, there is a lot of skill in selecting and using spells which do not depend upon a high Magic Power for effectiveness. Golemancy, for example, summons the same Golem regardless of Magic Power. Teleport, Sleep, and Shove do great things regardless of your Magic Power.
But the biggest oddity is the fact that some non-spells are still considered, by the game logic, to be "spells" - and thus key off your Magic Power. For example, many traps deal more damage to you if you have a high Magic Power. This makes Wizard characters especially prone to trap death, and means that Warrior characters can actually protect themselves by wearing armor which reduces their Magic Power!
The most important aspect of your character - and the one which will drive all of your primary & secondary stats - is your skill selection. Your skill distribution determines your archetype (Warrior, Wizard, Rogue, or Hybrid) and it also provides you most of the essential tools you will need to survive in the dungeons. Equipment and components you randomly find will be important as well - but you can't control them.
Warrior Skills: Swords, Axes, Maces, Staves, Unarmed Combat, Dual Wielding, Shield Bearer, Berserker Rage, Master of Arms, Smithing, Big Game Hunter(RotDG), Killer Vegan (RotDG). Clockwork Knight(YHTNTEP), Battle Geology (YHTNTEP) (14 skills)
Wizard Skills: Vampirism, Golemancy, Fleshmithing, Mathemagic, Psionics, Necronomiconomics, Viking Wizardry, Astrology, Promethean Magic, Magic Training, Blood Mage, Ley Walker, Alchemy, Wand Lore, Emomancy (RotDG), Warlockery (YHTNTEP) (16 skills)
Rogue Skills: Archery, Thrown Weapons, Artful Dodger, Perception, Burglary, Assassination, Fungal Arts, Archeology, Tinkering, Werediggle Curse (RotDG), Piracy (RotDG), Demonology (RotDG), Rogue Scientist (YHTNTEP) (13 skills)
The first seven skill selections are your weapon skills - they give you mastery over different combat styles. Archery and Thrown Weapons are pretty terrible as primary methods of dealing damage, so there are really just five combat skills to choose from. Every character needs to take one (and only one) of these skills. If you want to be a pure mage, you can safely skip these options - but you better have a really good plan!
Update! With the removal of the "bad weapon penalty" - it is now very viable to make a character without any weapon proficiency! You still really want weapon proficiency skills if you are looking to focus on a specific defense mechanism (counter chance for swords, criticals for axes, etc) and weapon skills are probably the best way to increase your warrior stats, so if you want to melee you want them just for that. Warriors might even want to mix 2 or 3 weapon skills - but don't try to mix "unarmed" with any of the others!
The next seven skills are mostly defense skills which improve your ability to survive combat. Dual Wielding is the exceptions - it is the "kill enemies quickly to survive longer" skill.
The next eight skills are the eight schools of magic. Every character should really take at least one of these - to make use of your mana. Two or three can be a good idea, but more than three is almost certainly a waste of your time.
The final twelve skills are "support" skills - which improve the function of your character, but don't really provide much direct benefit on their own. More Mana, stunning melee attacks, free mushrooms, better wand use, a sweet hat... The most important support skills are the three "crafting" skills - Smithing, Alchemy, Tinkering. These skills allow you to convert various items you find into other, more useful, items. Taking one of these skills can be fun, but taking more than one is usually an exercise in frustration, due to the amount of crap you'll be carrying around.
Update! Wand Lore is now a "crafting" skill - but it doesn't really fulfill the same role as the other crafting skills. Consider it for healing + ranged damage.
Each skill set has between 5 and 8 skills within it. You begin knowing the first skill from each tree you selected, and with each level you may unlock one additional skill. You won't be able to unlock every skill from every tree by the end of the game, so you will mostly focus on about 3 skill trees, and use the others only for their first or second-tier skills. Good candidates for "ignored skill trees" are those trees which give you a good bonus as their first skill - Artful Dodger, Master of Arms, Deadshot, Perception, and Tinkering are the stand-outs here. Other good candidates are those trees which give you a useful ability from the outset - Fungal Arts, Assassination, and Burglary.
Don't overlook the stat bonuses as potential gains, either! Selecting even 1 Warrior skill will start you with +1 melee power, which is a BIG help in the early game. Every wizard skill you select is +2 mana - even if you never take another Wizard skill again. Rogue skills improve your ability to hit enemies a bunch, even if you don't use the skills associated with them.
In Part 2, I'll go over each skill set explicitly.