Codex Martialis is a unique product built for the Open Gaming License/3.5 community. This is a combat supplement that turns whack-a-mole grind-fests into dynamic, exciting—and deadly—contests. Codex Martialis is based on real historical fighting techniques described in manuals from Medieval and Renaissance fighting masters, whose martial arts are being brought back to life by small groups of modern practitioners around the world. I was very excited when I found out about Codex Martialis, because to me, the usual d20 combat just wasn't that exciting anymore. Codex Martialis introduces three critical things that make combat truly exciting again.
First, it makes combat really deadly. Face it, traditional d20 combat can get pretty stale despite all the bling of magic weapons and nifty feats, because no matter how you cut it, all you're doing is slowly whittling away hit points. Seldom is there a real sense of danger, especially at higher levels. Codex Martialis changes this by suggesting a realistic hit point ceiling and making critical hits more frequent and potentially more dangerous, just as in real melee combat. Second, it requires the player to fight smart, not just because of the increased danger, but because it literally takes some smart, strategic decision-making to win. Knowing your own abilities and the strengths and weaknesses of your enemy's weapon, armor, and strategy can make a real difference in your ability to win. Third, it allows you to customize your fighting style based on your weapon and your chosen feats to make every fighter truly a unique force on the battlefield. The clash of different fighting styles makes for a different battle every time.
The meat of the system is pretty straightforward, although it can take awhile to get used to. Rather than a single d20 die, Codex Martialis fighters are given a pool of d20s, up to four dice, to use throughout the round. You can use these dice to make multiple single-die attacks or combine them into bigger multi-die attacks. The single-die attacks are pretty much business as usual. With the multi-die attacks, you roll however many dice you've chosen, say three, and take the highest result. This drastically increases your chances of getting a hit or a critical hit. In addition, you can take a standard movement action by spending a die. You can also keep dice in reserve and save them to roll as defense when you get attacked. When making a defense roll, a natural 20 (or a natural 1 by your opponent) means your opponent missed and also allows you to make your own attack out of turn! Rolling a tie triggers certain special abilities that I won't get into here. What's great about this is that it makes combat much more dynamic. You get don't have to just sit there and cringe while the DM rolls an attack. You get to actively participate in your defense. Fights feel like the natural give and take of real duels instead of a repetitive turn-taking exercise.
Those are the basics, but there's much more. For example, each weapon gets special bonuses depending on your range. Spears and longer weapons get special reach bonuses in the opening stages of a fight. Daggers and other short weapons get a big speed bonus when you've closed to grappling range, while the longer weapons get penalties until you back away again. Armor acts as damage reduction rather than adding to your defensive bonuses (more encouragement to save your attack dice for defense!).
And here's the true genius of the system: the so-called Martial Feats. These are special feats that are meant to model those real historical fighting moves I mentioned earlier. For the most part, they take advantage of the dice pool concept by granting additional dice in certain circumstances, but others give you additional attacks, or give you special techniques for taking advantage of your or your enemy's weapon and fighting style.
Codex Martialis also contains rules for archery, mounted combat, animal/monster attacks, and integrating spellcasting rules.
What about the book itself? It's is a PDF that's reasonably well designed, if a bit plain, and illustrated with simple line-art drawings taken from the aforementioned fighting manuals along with a few classical paintings and some other sources. The line drawings may seem a little strange at first, but they do add a sense of history to the book. The book reads well for the most part. It could use a little bit of editing attention, but there's nothing terribly wrong and it still holds up quite well compared to other similar products. Considering the great content, the current price of $10 is a bargain for what you get.
My only real criticism is that some aspects of the system have a bit of a learning curve—at least, they did for me. It can take a while to get used to the dynamic nature of the dice pool (do I use all my dice? keep some in reserve?) and to remember how the various armor and weapon stats apply. But even more than that, the expansive new feats can be almost overwhelming at times. It was hard to figure out which ones to choose and which ones work well together to represent a given fighting style. For example, I wanted to make a spear fighter, but it took a while to figure out which feats were best suited for the style of combat I wanted my character to have. On top of that, many of the new feats are named according to their non-English descriptions from the historical sources I mentioned above. Most of them have translations provided, but it could be a bit of a turn-off for those who aren't familiar with other languages.
One more thing I wanted to mention. The author of these supplements maintains an active forum for Codex Martialis and its companion supplements. He's very active and responsive on the forums, which I found refreshing. It's not like some supplements where you're left to your own devices. With this book, you get a small but helpful community of like-minded gamers, not least the author himself, who are willing to answer questions and help you out. That just makes the book worth even more in my eyes.