Critical hits are fun. Players enjoy big, flashy unusually good events. Some enjoy them so much that they play systems where they can narrate them right in, instead of waiting for the dice to serve them up, but that’s a topic for a different day. This was driven home to me when I was running games with my home-brew. It was a skill + roll system based around 2d6 but didn’t contain criticals, automatic hits, or fumbles. Every time a 12 came up there was a murmur of excitement around the table, followed by a sigh of disappointment when the players realized that it wasn’t a critical hit–in fact, due to the slightly unusual way the dice were read*, a 12 was usually a failure. After a couple of months I finally gave the players what they were looking for and made 12 a critical hit, giving max bonus and a special result on top, and the cycle of Woohoo! Awwww…. was over.
Critical hits are one of the first things that DMs think of adding to an otherwise fairly abstract combat system like D&D, and some games became notorious for their critical hit charts. Since they only get rolled once in a while, it’s possible to have a big chart with really detailed results without slowing things down much at all, and the chance of getting, say, a broken arm instead of just 8 hit points gave combat a grittier feel that a lot of players really appreciated.
The biggest problem with critical hits is that in combat heavy games there’s a built-in asymmetry between the PCs and the NPCs even if they’re using the same rules. PCs get a lot of dice rolled against them during the course of a campaign–orders of magnitude more than any individual NPC that they might encounter–and depending on the system they may well get more rolls against them than they make even in an individual combat, between often being outnumbered by the monsters, many monsters getting multiple attacks per round (the infamous claw/claw/bite) and PCs usually having lots more hit points before they are rendered hors de combat (once you figure in magical healing). That means that even really unlikely events will eventually hit the PCs, and on the whole the PCs will take more criticals than they dish out. At which point the rules that were originally added to give the players some more WooHoo! end up serving up heaping helpings of Oh Crap! instead. Insta-Kill crits are particularly unpleasant in this regard. And, as commenter Scott said over on the post Making Critical Hits More Interesting at Inkwell Ideas “a smashed ankle matters very little to the NPC who’s going to die in a couple of rounds, but very much to the PC who’s going to suffer until he can get a heal cast.”
A second, lesser, problem is that with systems that keep criticals fairly abstract (say, by awarding double damage but no extra result beyond that) it’s possible to get a critical hit but follow it up with a disappointing roll for damage…the fact that you’ve done 2 points instead of the 1 you would have rolled is cold comfort, and in terms of the emotions that rolling dice have added to the experience, you’d probably be better off not having rolled a critical in the first place. It becomes an artifact of the abstraction mechanism rather than a proxy for a game-world event; in the game-world it’s presumably not “My arrow hit him in the eye slit!….But it doesn’t seem to have slowed him down any….” And if that’s at all a common result of rolling a critical, you have to start asking whether it’s really worth having them in the game.
So, my suggestions for treating critical hits in games like D&D are as follows:
- Have them be something PCs do to NPCs, not vice-versa. Or, if symmetry between PCs and NPCs is important to you (so there’s no “PC glow”) then at least have the NPCs criticals do abstract damage, such as double damage, instead of rolling on a chart for specific results such as limb amputation. Otherwise you have to be prepared for most PCs to die or suffer career-ending injuries a lot sooner than their toughness as measured in hitpoints and armor class would otherwise indicate.
- If you want to have PCs sometimes face the possibility of a long-term or crippling injury, tie it to something less common than a 1 in 20 shot critical hit. One neat idea (borrowed from Savage Worlds) is tie it to the PC becoming incapacitated. In D&D that would mean getting knocked down to zero HP. Whenever the PC hits 0, then roll on the injury chart (possibly the same chart as the PCs have been dishing out to the NPCs); have the penalties for the injury persist even in the face of magical healing unless extra time and a Healing skill roll is made, or a more special-purpose spell (such as regenerate) is used. If you just slap Cure Serious Wounds on somebody with a shattered ankle, they get the hitpoints back and can fight again, but the ankle has been healed crooked.
- If you’re using abstract damage criticals, either just award max damage for the dice (so a crit on a d8 weapon automatically does 8 points, which is about the expected value of rolling 2d8 anyway), or if you insist on rolling have a minimum of the expected value. E.g. Roll 1d8 and multiply by 2, but have it be 9 points minimum (2 * expected value of 4.5) so that you avoid the WooHoo! Awww phenomenon.
* instead of adding the two dice, you used whichever face was lower. Doubles were zero. This yielded results from 0 to +5, weighted towards the 0 end; this meant you always performed at least as well as your skill (a concept borrowed from CORPS) so you never had to roll for tasks with DC <= your skill, but you had a decent chance of getting slightly better than that up to a slim chance of getting much better. But double-six counted as zero…bummer. The revised version had double six count as a +5 and a special result. It barely changed the expected value, but had a big impact on the excitement that players got from rolling.