Mental Energy

Mental Energy is a hard to quantify unit of cognitive power that can be used by a Magic user when casting Spells. When mental energy is depleted, the user will have to take a short break (could be 3 seconds to up to a minute depending on Mental Recovery) to recharge mental energy from their Mental Reserve, much like taking a short, immediate break from a boxing match before getting back in.

The reason it is hard to quantify in concrete numbers for several reasons.
 * There are many variations on how magical spells can be cast. One can decide to Detect Lifesig up to a 1 kilometer range, which will drain far more mental energy per second than an equivalent Detect Lifesig up to a 1 meter range.
 * Every magic user has their different stats that affect how much of a certain spell they can cast, so it is hard to compare by getting a magic user to cast a spell.
 * In addition, every magic user has a different level of understanding of a magic spell in terms of theoretical knowledge, which directly correlates to how much mental energy the spell takes to cast
 * To add further complication, magic users can only give fuzzy words to describe how much of their mental energy is currently available, much like one would not know that they have say, 23% stamina left - because it is hard to determine.