Material (M) Spell Components
Some spells call for material (M) spell components. These are required for that spell to have a 100% success rate; otherwise, for each missing material spell component, there is a cumulative 10% chance the spell "fizzles" or "misfires" in some (usually non-beneficial) manner.
For certain spells at DM's discretion, the listed material (M) spell components will be replaced by one or more of the Five Mystical Substances. In layman's terms, certain spells require shamanic drug use in order to activate the spell's effects.