I really enjoy the simplicity of the Black Hack’s “roll under attribute” mechanic, but I didn’t like having to apply modifiers for level difference on every interaction with monsters; nor the abscence of AC. This was my solution. It’s not quite as simple but requires minimal arithmetic and provides some additional information about the degree/type of success or failure. Did you fail to dodge because the monster was fast, or because you’re a klutz?
To make a test, roll 1d20. If you have advantage or disadvantage, roll 2d20 and take the better or worse roll, respectively.
The higher you roll when making a test, the more daring, aggressive, clever, or ambitious your effort was. The lower you roll, the more cautious, mundane, or timid the effort was.
To succeed you have to roll within your attribute score and over the difficulty. If you roll over your ability, you fail because you tried a little too hard; your effort exceeded your skill. If you roll equal to or under the difficulty, you failed because your effort was inadequate to overcome the opposition.
A natural 1 means you blanked out, froze up, or stumbled; it’s always a failure, and may cause additional complications; a 1 on a defense roll means taking a critical hit. Similarly, a 20 is an attempt so daring and lucky it succeeds regardless of your aptitude, and may provide additional benefits; a 20 on an attack roll deals a critical hit.
Many tests will have no difficulty, as there is no particular opposition. Conversely tests opposed by another player have a difficulty equal to their die roll, as long as it doesn’t exceed their ability.
Modifiers & Ability Scores Over 19
Modifiers always add to your attribute score for determining success. If this would take your attribute over 19, every excess point reduces the difficulty by 1. So, for example, an 18 STR fighter with a +3 sword hits an AC 5 monster as though it were AC 3.
This bit is sort of clumsy but not too bad in practice; it just means highly capable characters stop looking at their attribute and start looking at the difficulty.
Types of Test
|Attack Roll||STR (melee) or DEX (ranged)||Monster’s AC*||Deal your damage on a success.|
|Defense Roll||AC (DEX modified by armor)||Monster’s HD||Take damage on a failure.|
|Saving Throw||Any||Casters Level/None||Suffer effects, or more severe effects, on a failure.|
|Effect Roll||Usually INT or WIS||Target’s HD||Spell takes effect, or more severe effect, on a success.|
|Initiative Roll||DEX||Usually none||Act before the monsters in a round.|
|Surprise Roll||WIS||Usually none||Act in the first round of an unexpected combat.|
|Morale Test||CHA||Monster’s HD||Monsters flee or surrender.|
* Monster AC is an ascending number equal to 10 - [old school AC] - so a monster with AC 3 in traditional games has AC 7 here.
Your thoughts? Have you ever tried using an over/under system for rolls, or any other unusual method?