Rule: Marginal success and failure on checks
Replaces: Pass/fail check system
In Use In: None at this time; presented for consideration
Summary: Rather than a simple pass/fail system for checks, it is possible to partially succeed or partially fail.
In the 3.5 world, under most circumstances, you succeed at something completely or you fail utterly. Most situations in which skill checks are used, however, are not so cut-and-dry. When jumping across a chasm, you might clear it easily, or you might jump short and grab onto the far edge, dangling precariously. Both are technically successes, but one is clearly less of a success than others.
When using the Marginal Success rule, whenever you beat the DC by less than five, you have scored a "Marginal" success. The specific consequences of that marginal success are up to the DM, but will usually involve some minor penalty on top of the success. In the example above, perhaps you catch the far side of the gap by your elbows, but your sword goes clattering from your grasp; or, perhaps you land off-balance and fall prone.
Not every skill will have a chance of marginal success; generally, only pass/fail skill checks are covered. A Knowledge check, for example, generally has margins already built in, as does Appraise. A marginal success on Bluff might give your opponent a bonus to Sense Motive for future rolls; a marginal success on Perception might allow you to notice that something is up without giving away too much information. A marginal success on Acrobatics might give a bonus to AC versus attacks of opportunity instead of negating them entirely.
Just like barely succeeding, sometimes you almost succeed but don't. While there are times when this "almost" doesn't matter, there are other times that it does.
If you fail a check by less than five, you have achieved a marginal failure. The general consequence of this is that you have failed, but the repercussions of doing so are not as severe as they otherwise would have been. If you marginally fail to jump across a chasm, rather than falling to your death, perhaps you simply drop what is in your hand down the pit. If you marginally fail a Negotiation check, the other party might respond with a counter offer rather than refusing outright.