If a spell has a duration, it lasts a number of rounds equal to your level, plus 1 round per MP spent to cast the spell. For example, if you are 3rd level and spend 2 MP to cast a spell, it will last 5 rounds.
If the spell has targets, it can affect a number of targets in its area of effect equal to the MP spent to cast the spell.
Area of Effect
Scaling Spell Parameters
Note that each of these parameters scales together with the MP you spend. So if you spend 2 MP on a spell and you're 3rd level, the spell lasts 5 rounds and affects up to 2 targets in a melee space.
Unless the spell says otherwise, you cannot change the parameters of a spell after it has been cast. That is, if you spent 2 MP to cast a spell, you can't add more MP to increase its duration once it's cast.
Line of Sight
Spells are cast at line of sight, unless they say otherwise. If you can see the target, and it's within the spell's area of effect, you can cast a spell on it. Some spells may require you to touch the target, which is considered a touch attack if the target resists you.
Some spells may require you to touch the target in order to deliver the effects of the spell. This means you must succeed in a Hand-to-Hand attack against them in order for the spell to take effect. The victim is then entitled to a spell check to resist.
Area of Effect
A spell’s area of effect is described by the physical space it affects. Spells by default have an area of effect equal to your personal space. The more MP you spend casting a spell, the greater the space the spell affects.
- Personal (1 MP). The spell affects a volume of space equal to your personal space (so, about a meter across). This space can only ever accommodate a single character, or anything within that character’s reach.
- Melee (2 MP). The spell affects a volume of space equal to an area encompassing several opponents. This is likely 10 meters across but never more than half the size of the encounter.
- Encounter(3 MP). The spell affects a volume of space equal to an entire scene. Think a football field or a large clearing.
Keep in mind the units of measurement above are provided only as examples. If the encounter space is a living room, then the units of measurement would be very different in each space!
Moreover, the area of effect can be any three-dimensional shape, as long as the shape is unbroken and continuous.
Spellcasting has an obvious visual and auditory effect. Even though the psychic does not need any components to use their powers, their eyes might glow and there might be a strange whooshing or popping sound that occurs when their powers are invoked. Clerics may need to loudly incant their scriptures to cast miracles, while mages may need to draw elaborate, glowing geometry on a nearby surfaces to manipulate sorcerous energies.
The exact details are up to you to decide, but the bottom line is that unless you have an ability that makes your spellcasting stealthy, spellcasting is a risky action that's as noisy and obvious as swinging a long sword while wearing chainmail or pulling the trigger on a loud firearm.