As opposed to standard 'saves' in which there is an aggressor trying to
overcome some innate ability of the victim (Resilience, Fortitude, Reflex),
some abilities simply have a 'Difficulty Class'. 

   Skills with a difficulty class have a number that you must roll higher
than to save against their effect.

   E.g. Hemlock Poison has a Difficulty Class of 20. That means when a rogue,
whose weapon is poisoned, strikes you, you must roll greater than 20 on a 1d100
or else suffer the effects.
such as "spell" or "MUD Basics"
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