This is a compilation of the different ways spell systems can work in games. The emphasis is placed upon video game RPGs, but developers of other types of games may find this article useful as well.
Each spell has several parameters. Most games will use most of these parameters in some way. Some possible parameters are listed below.
Casting a spell typically has some sort of cost. If it didn't, people would just zap everything in the game and win immediately. Various possible costs are listed below.
Corruption: When the caster uses a spell, he becomes slightly corrupted. Over time, the caster mutates into a demon.
Gold: Casting a spell expends gold. In games using this type of spell cost, "spells" are usually called something else.
Items: Casting a spell expends an item (e.g. elixirs, potions, scrolls). Some items may be usable more than once (e.g. rods, staffs, wands). In some games, casting a spell expends more than one item - in these cases, you assemble a number of items (a.k.a. spell components) and somehow combine them into a spell. This is often used as a supplement to another magical system, but there are some games where the items are the spells.
Maintenance: In addition to the initial effect, the caster must also maintain the effect by spending a percentage of the spell cost during each minute the spell is in effect.
Pollution: Casting spells causes some sort of radiation or evil presence in the area. The more spells are cast (and the more powerful the spells are), the worse it gets. Enemies mutate and become stronger. Harmless people go crazy and attack. Inanimate objects come alive and bite you. Gateways open to hell.
Sacrifice: Evil characters murder other characters to allow them to cast a spell. Alternatively, good characters sacrifice themselves. In most cases the sacrifice is performed when the spell is cast, but a good character might cast a spell to become invulnerable for a time and then die when the spell ends.
One-time Casting: When the character learns a spell, he can cast it once. When a spell is cast, it's forgotten. It is, however, possible to learn the same spell more than once simultaneously. What spells the character knows are chosen by one of the following methods:
Spell Points: A character has some number of spell points, and each spell costs a certain number of spell points. A character expends spell points every time he casts a spell and can't cast any more spells when he runs out of spells points. Spell points are restored in one (or more) of several ways: a) they regenerate over time, b) they are restored by one-use items, c) they are restored by resting, d) they are restored by going to a special location, e) they are restored by defeating enemies. With a spell point system, you can cast whatever spells you want as many times as you want, so long as you have the spell points required to cast them. Some alternatives:
Faith: Spellcasters gather "faith" from other creatures. It's either faith in some sort of deity that the caster serves or faith in the caster herself. This faith is then expended to cast spells. There is no maximum to the amount of faith a character can gather.
Level Loss: The caster loses a level. This is generally reserved for games where death is final (i.e. if you die, your character is erased), and, even then, it's only used for getting your characters' fat out of the fryer.
Thirst: In cases where characters "sing" spells, they can get thirsty. To regain their singing voice, they have to drink something. This is appropriate for "bard" characters who cast spells by singing.
Time: The spell takes a certain amount of time to cast. During this time, the caster is unable to do anything else and might be defenseless against enemy attacks. This is typically paired with some other form of spell cost.
Usage Frequency: There's no real cost, but the character can only use the spell once every so many minutes/hours/whatever. Alternatively, the character can use the spell 2 or 3 times per day (which is actually similar to Spell Memorization).
Spell duration can be determined in a number of ways.
The spell has to do something. Otherwise, what's the point?
The effect could be almost anything. For this reason, the entire World of Spells is dedicated to listing the possible effects of various spells.
There's only a few ways to determine the effectiveness of a spell:
Some spells have limitations that reduce the cost of the spell but make the spell less effective. Some potential limitations are listed below:
For spells that allow the caster to select targets, range is important. The range might increase as the caster becomes more powerful.
Typically, a beneficial spell isn't resisted, but hostile spells are. Some ways to resist spells are as follows:
Some spells only affect current kinds of characters (e.g. elementals, living creatures, undead, summoned creatures).
In many games, there are different "branches" of magic. Each branch uses a separate statistic to determine spell effectiveness and resistance to spells of that branch. Some examples are listed below.
Elemental: The spell branches are air/earth/fire/water. This is one of the more popular divisions. Combination spells can have cool names, such as "Rain" for an air/water spell.
Life/Death: Life magic heals, and death magic kills. There's not much confusion there. But then again, life magic often kills undead creatures, and death magic can often heal the caster by draining life from a target. In the Sword of Truth novels, these are referred to as Additive and Subtractive magic.
Psionics: Psionics is "mind" magic, though it's often considered to be technological in nature. Many games have cool psionic effects, but calling them anything other magic is just for the purpose of giving them a different name.
Wild Magic: What is wild magic? It's the same as regular magic except with more randomness.
One of the main problems with spell branches is that many games have spell branches that have spells that, essentially, differ only in name. If any game developers are reading this, please try to make spells that actually have different effects.
What follows is information that isn't central to the discussion. Most of it could have been included elsewhere in this document, but it would distract the reader from more relevant topics. Hence, it was dumped into this section at the end.
Some games contain spell systems, but call the spells something else. This is no problem. It really just amounts to changing the names of everything.
In some games, "spells" are actually innate abilities. This usually means that the caster can use them with relatively small costs, but the abilities usually aren't as effective. Sometimes, there's a limit to how often the abilities can be used.
In other games, "spells" are technological effects caused by using high-tech items. In some cases, this can be similar to using innate abilities, but in other cases it's more like a game where you have to use scrolls to cast spells. Of course, the "scrolls" will be called grenades or something.
These spells are just combinations of other spells. This allows you to cast a number of spells at once. For instance, an "Enhance" spell could cast the Bless, Haste, and Regenerate spells all at once.
These spells are useful because they allow to cast a whole group of spells at once, freeing you to take other actions.
These spells are cast jointly by multiple casters, each of whom expends part of whatever the spell costs. These spells are typically very powerful.
Multicaster spells are inappropriate for many games. They should only be used in games where characters choose their actions at the same time. One possibility to allow multicaster spells in other games is to allow "linking". Several casters link their magic, effectively transferring it all to one caster. That caster can cast the spells, and the rest of the casters are unable to cast spells. In some games, the secondary casters could be rendered unconscious.
Some spells have random effects. Some spells have a chance of failing. Other spells randomly backfire, affecting the caster (though perhaps with a different effect from the normal spell effect).
In general, the spell's cost is as follows: Cost = P(E1) * C(E1) + P(E2) * C(E2) + ... + P(En) * C(En). Ex represents the xth possible effect of the spell. P(Ex) is the probability of effect Ex occurring. C(Ex) is the cost of effect Ex.
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