All units have free abilities, they can be used whenever you have enough turn time left. However, the more powerful abilities have an additional cost: special points.
There are different types of special points, each kind has at least one unique characteristic that makes it different from the others.
A single unit can use only one type of special points, but abilities do not follow this restriction. For example, the same ability might be available to magic users and stamina users.
Let's see in detail each special point type.
Stamina
Stamina is the basic special type for common units. This doesn't mean that stamina based abilities are inferior to others: their relative low cost and variety are strong advantages.
Units regenerate stamina at the beginning of the turn. The regeneration rate depends on the condition of the body, in other words on how many hp the unit has left. An heaviliy hurt soldier will need much more time to gather the strength needed use his best abilities.
Magic
Wizard and other magicians have their own special type. Magic is characterized by huge versatility and good regeneration per turn. While it's true that often spells are very costly (much more than other kind of abilities), wizards have a slightly higher cap for maximum special points, allowing the use of few powerful moves before running out of magic.
Another downside of magic is the risk of being silenced: when it happens, the unit is unable to use spells until the effect wears out or is removed.
Fervor
Fervor is a resouce used mainly by knights. It originates from a strong sense of conviction and its regeneration is influenced by the unit's morale.
Fervor abilities are generally quite effective for a moderate cost.
Focus
Focus is the special type used by martial artists. It's quite different from the others for many reasons.
First, focus can't be regenerated during battle and the amount of starting points is usually very low.
Second, abilities using focus are free to use when not in cooldown. By spending focus points it's possible to use an ability that's currently in cooldown; it couldn't be used under normal circumstances.
Crystals
Units equipped with magitech weapons need crystals in order to operate said machinery. These weapons are very powerful but unfortunately they consume many crystals, which can't be regenerated; the only way to fix this issue is to recruit specialized units (mechanics) able to replenish the crystals' tanks of their allies.
Fury
Fury represents the power given by extreme anger. Few soldiers can use this power effectively in battle. Contrary to other special types, fury points starts at 0 and are gained only when the unit takes damage.
