Spells in OSR+ are written in a deliberately brief, precising way. This is for a number of reasons: brevity first and foremost, but also to allow for interpretation on the GM’s part, and creativity on the player's part. Each spell assumes that the below spell logic holds true, and will not reiterate any assumptions made here except to supersede them. Always remember: the GM has the final say on any rulings regarding spells.
Some spells may redefine the parameters of the spell as values other than what is described in the rules ("hours" per MP spent, or "miles" per MP spent). Only the parameters altered by the spell text apply—assume the default values otherwise.
The Cost of Spells
A spell always costs at least 1 to cast, even if it does not mention a cost.
Casting Spells Blindly
You can target anything you can see, provided it's in the area of effect (AoE). This does imply that if a spell does not require a target, you don't need to see in order to cast the spell.
More Powerful Than You
This language means a higher level than you.
Some spells may be used to indirectly cause harm. When in doubt, roll a d6 to determine the damage, and apply the secondary effects of an appropriate maleficence.
Stationary AREAS of Effect
Some spells describe areas of effect that emanate from you (or are implied to be surrounding you in some way). Unless the spell explicitly says the area of effect is immovable, assume the area of effect is centered on you and moves with you wherever you go.
Victims are always entitled to make a spell check to resist a spell, even if the spell does not explicitly state this. If the victim successfully resists, the spell does not affect them and they need not check again until the next time the spell is cast against them. Spells may specify a particular attribute to use in a check; if so, use the attribute the spell specifies. If nothing is specified, use the attribute that corresponds to the spell's magic type (Mighty for psionic spells, Deft for thaumaturgy, Smart for sorcery).
SPell Checks & Spells Without Targets
Spells without targets only entitle victims to resist when they violate some dictate of the spell. For example, a spell like Charm (Monster) entitles the victim to resist the spell when it is cast, whereas a spell like Zone of Truth has no target, so victims in the area of effect are not entitled to resist the spell until they attempt to lie. Victims only get one chance to resist, unless the spell requires active concentration and is continually incapacitating or stunning its victims.
Effects on the Caster
Any harmful effects that are a direct result of your spells don't affect you, unless the spell says otherwise. This is also true for the spell’s effects that you do not want to affect you, unless the spell says otherwise. This does not include mundane perils that result from your spells' effects. (For example, if your spell caught something on fire, and you're now trapped in a burning building, the fire is mundane and will hurt you.)
Generally, once a spell is cast, it lasts for its duration and the spellcaster may take other actions while the spell is in effect. (With the exception of the Bard class, whose technique allows him to choose to make the duration of a spell indefinite, so long as he continues to concentrate on working the spell).
Some spells specifically require you to concentrate for the entire duration of the spell, or else the spell ends and your victims are released from its effects. Other spells may imply that concentration is necessary, but from a mechanical point of view these are considered directed spells (see below). For example, a spell like Ensorcell specifies concentration explicitly, whereas a spell like Control (Gravity) only implies it.
Taking Action While Concentrating
Concentration means you are focusing special attention on the working of your spell against the victim(s). While concentrating, if you cast another concentration spell or make an attack (or take any attack action, such as maleficence), the spell you are concentrating on immediately ends.
While you are concentrating, if you're successfully attacked (or receive any form of damage), the spell automatically ends. If your concentration is broken by other means (someone is distracting you or you're trying to do two things at once), the GM may grant you a Mighty check to maintain your concentration.
Some spells, while not requiring your concentration, require you to make decisions about what happens with their effects for the duration of the spell. For example, if you have cast Magic Monitor, you have control over the monitor for the duration of the spell. When you make decisions for the monitor, these decisions are considered reactions and don't use up your action in the round. The effects of spells directed in this way always happen once, whenever you're able to act in the round.
Spells do not require you to touch the target unless they specifically say so. If the target is unwilling to be touched, make a Hand-to-Hand attack against them to deliver the effects of the spell. They are entitled to a spell check to resist if you succeed in touching them. Failing to touch them means you were not able to cast the spell, and so the MP you invest into the spell are not lost.
Spells Without Targets
Spells tend to use the word “victims” and “targets” interchangeably. Victims are generally understood to be unwilling targets. If a spell says it affects anyone in an AoE without your having to spend MP against each victim (the victims are not countable), or the spell targets an AoE that in turn affects victims that are within it, then the spell doesn’t have targets, and so there is no additional cost per target to cast it. Even so, victims affected by the spell are still entitled to resist the spell's effects, unless the spell says otherwise.
Zone of Truth
Your magic expunges lies in the area of effect. Although they are not forced to tell the truth, anyone within the area of effect is unable to tell a lie.
This spell affects an AoE (it "expunges lies in the area of effect"), so it doesn’t target anyone in particular. A victim in the AoE is still entitled to resist when they violate the spell's dictates (lie), but whether there is a single victim or one hundred victims in the AoE, there is no additional MP cost per target to cast the spell.
If a spell specifically says "a single target" or enumerates any other parameter of the spell, then you may not increase the number of targets, or said parameter, by spending additional MP.
Types of Targets
Targets can be people or things, except when the spell explicitly says “objects” or is more specific about the type of target. Mundane means non-magical, humanoid means non-monstrous (which is inclusive of other humanoid origins besides humans), magical means supernatural in nature or effect. Living and dead are also important distinctions, as monsters of the type Undead are neither dead nor alive.
You vs. Other Subjects
The subject of the spell is the person who casts it, and from whom its effects emanate. Note, this is different than the spell's targets: a spell always has a subject, but may have a target. Spells may say "you do XYZ" or "you or your target does XYZ." This is deliberate: if the spell only mentions you as the source of its effects and does not mention other targets, then only you can be the subject of the spell.
Types of Spells
Spells with Inversion
Such a spell offers two effects that you may choose from when casting it. Each time you cast the spell, you may decide which effect to employ. Haste & Slow, for example, is actually two spells in one: each time you cast it, you may slow or haste your targets.
Some spells produce an instantaneous effect and do not have a duration. For such a spell, it does not make sense for a spellcaster to spend MP to increase its duration. Word of Undoing and Command are examples.
Spells with a Wager
A spell that offers a choice between effects for varying MP costs is necessarily being cast with the same amount of duration, AoE, and targets (if applicable) as the cost you choose. For example:
With magical insight, you enhance your vision to see through illusions and other non-magical falsehoods in the spell's area of effect. For 1 MP, that which is hidden is revealed. For 2 MP, you see through disguises. For 3 MP, lies sound false to you and written untruths glow magically.
If this spell were cast at 3 MP, then it would last for 3 rounds plus the level of the caster, and the AoE would be an encounter space. There is no target in this spell, as it reveals all illusions in the AoE.
Some spells may be cast outside your initiative as a reaction, provided you have not already acted in the round and have the MP available to cast the spell. You must declare that you are casting the spell prior to the GM's resolution in a turn, otherwise your action would happen after the GM's resolution.
Counterspells & MP
Spells or abilities that counter magic (such as the spell Counterspell or Spell Turn) require you to expend the MP required to counter the spell even if you fail to counter it.
Some spells let you change the past, but only insofar as whatever you change doesn't contradict the past GM resolutions: that is, your tinkering with the past can't invalidate what the GM has already ruled as having happened, or create a paradox in the present. For example, you might not be able to stop your friend from having been thrown off a cliff, but you can go back in time and cast Dimension Door below them so that they're now plummeting into a magical portal that will deposit them directly to safety.
With Time Stop in particular, resolve your actions while time is frozen before the rest of the party acts in the round, even if you are time stopped for multiple rounds (e.g, you cannot hold your turn to see what others do later in the round because all your actions within Time Stop resolve before they are able to act).
Some spells or abilities bring under your control summons, which are typically monsters or animals. If the spell does not specify the mechanics for the summon (abilities, attributes, attacks, etc), and the GM does not have in mind a particular set of stats for the summon, then assume the summon uses your stats for rolls and confer with the GM as to how to handle its unique abilities as described by the spell. Additionally, a summon or familiar whose HP or MP is not specified has 1d6 HP and 1d6 MP.
- Summoning Sickness. Summons enter your plane of existence in a state of bewilderment, and it takes time for them to come to grips with the physics of material reality, therefore a summon may not act on the turn it is summoned except to take defensive action.
- Astral Parity. Summons must maintain astral parity with you to remain on the material plane, unless the spell that summons them requires you to concentrate. If a summon leaves your line of sight for more than 1 round, it becomes unsummoned and must be reconjured by whatever means were necessary to conjure it in the first place. This is not the same as if it is slain, however, as some abilities will specify what happens when a summon is slain. For example, if the summon "requires 24 hours rest" to be reconjured when it is slain, then you may immediately reconjure the summon if it becomes unsummoned due to its leaving your line of sight for more than 1 round.
Your enchantment makes a single humanoid target friendly towards you and assuages their suspicions. When you are casting this spell, it is not apparent to the untrained eye. This spell immediately fails if anyone in the area of effect is engaged in hostile action with the victim or its allies, or if you or your allies take hostile action thereafter. When engaged in social combat with a charmed person, you receive advantage on all rolls. A charmed person maintains their disposition toward you even after the spell ends, unless there is reason to question the friendship or the enchantment is revealed.
A character's disposition is the way they would act under normal circumstances. A charm spell attempts to change a character's disposition, in some cases only for the duration of the spell, and in others, permanently. A charm spell is not mind control, nor does it deprive a victim of his free will, as is the case with the spells Command or Post-Hypnotic Suggestion; mechanically, Charm spells only enhance your social interactions with your victims (e.g., conferring advantage in social combat).
Charm Spells & Spell Subtlety
Charm spells may specify the following:
When you are casting this spell, it is not apparent to the untrained eye.
This means that the spell is surreptitious, and unlike other spells, has no obvious visual or auditory effect. Mechanically, this means the spellcasting can only be detected if the victim (or other observers) are already suspicious of the spellcaster at the time the spell is being cast. In this scenario, the victims would be entitled to a check so as to react to the spell before it's cast (provided they have not already been afforded that opportunity); the GM may then afford them a contested Perception check vs. a spell check from the spellcaster, which may trigger an initiative for all involved.
Charm Spells & Combat
Charm spells may specify further:
This spell immediately fails if anyone in the area of effect is engaged in hostile action with the victim or its allies, or if you or your allies take hostile action thereafter.
The purpose of this language is to specifically bar Charm spells from working when the victim, its allies, or the spellcasters' allies are engaged in combat with the spellcaster. Remember, a Charm spell merely attempts to alter its victim's disposition toward the spellcaster, and so the implication here is that the magic of Charm spells is not enough to change a victim's disposition when they (or their allies) know they are actively being harmed by the spellcaster, either directly or indirectly.