The obSESSION RPG Meta-System.

obSESSION's Core Mechanics

The universe is defined in obSESSION by a number of Attributes, a selection of which are used depending on the type of thing being described, and possibly a selection of skills. Everything you meet is also defined as either a Character, Monster or Artefact.

The Skill Roll
The Skill Roll is the most common die roll in obSESSION, being used whenever an action is attempted where the success is in doubt. This is done by rolling a number of D10s equal to the skill being used (effectively a roll of SkillD10) but instead of totaling the results they are compared individually to a Threshold Number (TN). The total number of dice that roll higher than the TN is the number of successes (sometimes called "level of success") that have been achieved.
In many cases the action requires only a single success to indicate a successful performance, but more complex actions may be judged based on the number of successes achieved. This applies when different degrees of success are possible, such as when playing darts (One success might hit the dart board while two hits the 20 and three manages a double 20).
On occasion the TN of a Skill Roll may be modified to zero or below, in these cases the roll is made as if the TN was 1 (ie. A roll of 1 on a D10 never counts as a success). There is an advantage to a TN lower than zero however : the absolute value of a negative TN (absolute value is the number without any plus or minus designation) is added to the number of dice rolled. Thus a Skill Roll with a TN of -3 is rolled with three extra dice, just as if the skill were three points higher.
One last rule relating to Skill Rolls remains to be explained. Whenever a die comes up 10 on a skill roll that die, in addition to counting as a success, may be re-rolled in an attempt to earn a second success. Such re-rolled dice are NOT rolled again if they roll a second 10.
Sometimes a Skill Roll will need to be made using an Attribute (this can be referred to as an Attribute Roll but since it is mechanically identitcal to any other Skill Roll there is little point in giving it a separate name). These rules are no different from any other Skill Roll, but the Attribute's Skill Value (see Chapter One) is used in place of a Skill's Rank.

Combined Rolls
Sometimes an action using an Attribute can also be affected by skills and these cases a Combined Roll is used. Combined Rolls involve the use of an Attribute based Skill Roll (as described above) and a relevant Skill Roll (assuming that the C/M/A possesses the Skill in question), with the two Success Levels totaled to provide a final result. Since it makes no difference to the end result a player can make the two halves of a Combined Roll separately or can total the number of dice rolled according to their own preferences.

The Saving Throw
The other roll commonly made in obSESSION is the Saving Throw. Saving Throws are all-or-nothing checks for success, usually made to resist some influence that may or may not affect the C/M/A and are made by rolling 1D100 against one of the C/M/A's Attributes. The most common type of Save is made against the Full Value of an Attribute, this is also known as a "Level 3 Save". The Level of a Saving Throw (also known as the Required Save Level) determines the percentage of Full Value that the Saving Throw is rolled against.