A while ago I mentioned that I used to like skill systems which incorporate partial success/ partial failure, but now I am not so enamoured of them. Since I wrote that I had to rejig my magic system slightly, because I had configured it to be a little too easy. As my magic system was constructed, every spell came with a casting DC. Beating the DC meant that the caster cast the spell with no fatigue, and the degree of success determined by the amount over the target DC which the player rolled, subject to some maximum (which partially determined the spell DC). Failure to beat the DC meant the spell was cast, but the caster suffered fatigue; in some cases the spell fails and in all cases, the save DC of the spell is the player’s roll.
The problem with this system is that one of the characters in my system has the spell Grendel’s Demise which rips off a target’s arm; and another has The Angel of Death, which just slaughters everyone in sight. With no risk of not being able to cast the spell, these characters get to basically try and kill one monster every round, at risk of a mere fatigue.
So I introduced a new rule for failures: if the player rolled lower than [casting DC – level] the spell automatically failed, and the character suffered fatigue. Grendel’s Demise has a spell DC of 23 and the characters are 5th level, so any roll of 18 or less means the spell completely fails. As the characters gain levels, the risk of complete failure decreases. This means I can continue to give low level characters very dangerous spells, knowing that they won’t use them unless they’re really desperate, until they’re high enough level to guarantee success.
But this new system introduces partial failure into the system. Given that the system already allows for partial success, this means I have essentially reproduced the Rolemaster skill paradigm (minus a lot of categories and tables of course).
Consider, for example, a 5th level wizard with magic skill of 8, casting a 4th level spell (casting DC 19) which stuns the opponent for 1 round per point of success. Partial success with this system is always possible; for example, if the caster rolls 19 the spell is cast with no fatigue, and the victim has to roll over 19 on a saving throw or is stunned for 1 rd per point of failure. Partial failure occurs on rolls of 14-19; in this instance, the target still has to roll to save, but the roll is easier, so there will be less rounds of stun (on average) and the caster takes a fatigue. On rolls less than 14 there is complete failure – caster incurs fatigue, spell never happens, victim never notices.
At first I thought that this would only apply to magic but now I realise it can be applied across the entire skill system. Consider, for example, a 3rd level thief on a rooftop who decides to do a sneak attack by dropping off the roof onto a passing guard. Adjudicate this attack thus: the rooftop attack could give a maximum +2 damage, so the DC is 19 (15+2*maximum effect is my current guideline). The actual effect is determined by the player’s acrobatics roll minus the DC, with a maximum of +2. On rolls of 16-19 the character can still attack but is judged to have landed badly and attacks at a penalty equal to [DC – roll]. Anything less than 16 and the character takes damage and loses the attack.
Note also that under this system the maximum penalty a character can take is limited by their level, which makes me think that levels can also serve to put a limit on the maximum benefit a character can gain (and thus also the maximum DC they ever have to beat). This ties the skill system and the levels together more tightly than just allowing levels to determine skill points. In my system this means that a character’s development, saving throws, skills and actual DCs are all joined together through the skill system and the level system.
And note that none of this is incompatible with D&D3.5 or Pathfinder or whatever. This is another example of how, I think, the D20 skill system is a really natural and flexible way to resolve all the actions which characters face. You really don’t need anything except skill points and levels!