Spell Focus

Spell Focus is a term that refers to when a Magic user actively is focusing on actively casting a spell. It is very difficult to focus on two spells at the same time, and the closest thing one can get is rapidly switching focus between them.

Advantage
Focusing to cast a "primary" spell has the advantage of saving a lot of Mental Power, up to 50%.

Only one spell can be focused on at a time - other active spells need Automaticity
However, if more than two spells need to be active at the same time, Automaticity is the only way to truly perform this, because some spell combinations cannot be switched between rapidly enough to maintain them properly.

Switching Spell Focus takes time, or else extra Mental Energy is used.
Switching spell focus comes with its own cooldown dictated by Mental Flow. For example, if a user has an average mental flow, they may take up to 2 seconds to properly switch between spells, as they have to bring to their focus how the other spell is cast. If that user attempts to cast before that 2 seconds, they will get a penalty. For example, if 2 seconds is their switch speed and they cast the other spell prematurely at 1 second, they will get a (2/1)*100 = 200% penalty to the Mental Energy cost of that spell. This is capped at a 400% penalty.

Examples
An example of such a situation where it would be impossible to switch rapidly enough is Levitate + Telekinesis at the same time - if you focus on just the telekinesis, you'll fall, and then if you focus on the levitation, the object you're holding will fall)

On the other hand, switching between firing Ice Spike and Detect Lifesig would still be feasible.