How to Cast Spells
Magic is woven through the worlds, like threads - even called "The Weave" by scholars and priests. Casting a spell is like strumming the strings of an instrument to make a sound, but instead making an effect in the world.
Spell Level
Each spell has a level, just like character classes have levels. Just as characters are able to do more difficult things and it takes practice to get to those levels, the levels of spells indicate how difficult they are to learn and use. Casters are given a budget of slots with corresponding levels they can use to fuel spell powers.
Retired: The power of a spell is based on the "mana" (tracked by MP) used to fuel its effect. A caster must spend MP equal to 1 + the spell's level to make it work (so a 3rd level spell would cost 4MP). Homebrew MP System (GM Binder) or (PDF)
Sorcerers & Warlocks
As a DM, I've not yet really digested the Sorcerer class, so for now Sorcerers do not exist in the realms.
Warlocks can cast a certain number of spells until needing a short rest. Spells cast by a Warlock are always at the full "upcast" level of power according to their level.
Upcasting
Spells may be "upcast" to deliver more powerful effects than what they are capable of when first learned. This is accomplished by fueling the casting with a higher level spell slot. Spell descriptions will specify the additional effects in descriptions such as "when cast at higher level". The maximum spell slot available depends on the slot pool for the class and what has already been used.
Cantrips
Cantrips are magical effects that are learned with heavily repeated practice and cost no spell slots to cast. They can be thought of as Level 0 spells that gain in power corresponding to the level of the caster (rather than adding MP). Like with proficiency, multi-classed characters use their total levels rather than level within a class to determine the casting level.
Rituals
Some spell descriptions note the spell may be cast in a complex time-consuming manner called a "ritual". Bards, Clerics, Druids, Wizards and some Warlocks are able to perform ritual casting. One advantage of ritual casting is that it does not require using a spell slot (but does not upcast). The casting time is generally increased by 10 minutes, but may be longer for complex spells. Ritual casting requires having the spell prepared, with the exceptions of Warlocks (any ritual spell from their Book of Ancient Secrets) and Wizards (any ritual spell from their spellbook).
Spell Scrolls & Magic Items
Casting a spell from a scroll or magic item does not require knowing the spell or supplying any MP. These are supplied by the spell scroll or item. Scrolls may be used by any class (even non-casters) so long as they can read the spell scroll. Spell scrolls are "consumed" (used up) by the casting. Magic Items usually have a limited number of "charges" or uses in a time period. Note a wizard may copy from a spell scroll into their spellbook to learn a new spell (which uses up the spell scroll in the process). Flutes Loot wrote a good guide to spell scrolls.
Prepared Spells
The only spells ready to be cast are those selected as "prepared" in the mind of the spellcaster. For some classes, all known spells are always prepared. Other classes must choose which spells are prepared after a long rest, selecting from a longer list of spells that are "known". Sometimes a subclass or race ability allow a spell to always be prepared (and not count against the limit of prepared spells).
Clerics & Druids
- Select a limited number (WIS mod + level) of prepared spells from the full list of spell options for their class (knowledge supplied by their deity).
- This list of prepared spells can be changed after each long rest (requiring 1 minute per spell level of newly-prepared spells).
- Any spells may be upcast using more MP (up to the power of the highest level spell they can learn).
Warlocks
- All known spells are also prepared and ready to cast.
- The number of known/prepared spells may be reselected when gaining a level, up to the number listed in the Warlock class table.
- All spells are upcast to the power of the highest level of spell they can learn.
- There are additional rules for the Pact of the Tome subclass.
Wizards
- Select a limited number (INT mod + level) of prepared spells from those copied into their spellbook (their learned/known spells).
- This list of prepared spells can be changed after each long rest (requiring 1 minute per spell level of newly-prepared spells).
- Any spells may be upcast using a higher unused spell slot (up to the power of the highest level spell they can learn).
- The Wizard's Spellbook
- May be lost, stolen, or destroyed - potentially losing knowledge of spells if not saved in a backup copy.
- A backup copy may be made: add together all the levels of spells in the book, then it will take 1 hour and 10gp in materials per each of those total levels.
- When gaining a level, two spells (of a knowable level) may be copied into the spellbook at no cost.
- New spells may be added by spending 1 hour and 50gp for materials for each level of the new spell being copied into the spellbook.
Bards, Paladins, Rangers & Others
- All known spells are also prepared and ready to cast.
- The number of known/prepared spells may be reselected when gaining a level, up to the number listed in the Warlock class table.
- Any spells may be upcast using a higher unused spell slot (up to the power of the highest level spell they can learn).
- Consult the class table for the number of spells known (Bards are usually level+3, Paladins are half-level + CHA mod, etc.)
- "Others" are subclass types such as Arcane Trickster (Rogue) and Eldritch Knight (Fighter), see their descriptions for similar rules.
Casting a Spell
Selecting a prepared spell and spending the MP or slot to fuel the spell, the casting itself depends on the details in the description of the spell, in addition to the effects of that spell once it is cast.
Casting Time: Action, Bonus Action, Reaction
Unless it says otherwise, a spell requires using your turn's Action to cast the spell. Otherwise, if the spell description lists casting time:
- longer than an Action, it requires using every turn's Action until completed.
(If interrupted, you do not use up the MP/slot.) - as a Bonus Action, it can combine with a normal Action - but not for a spell unless a one-Action Cantrip.
(Usually Bonus Action spells add to an action like loading a damaging effect on an attack, or enhancing movement). - as a Reaction, the spell is extremely quick and since it happens outside your turn, you can still cast on your turn's Action.
(Reaction-cast spells are rare, the full list: Absorb Elements, Counterspell, Featherfall, Gift of Gab, Hellish Rebuke, Shield, Soul Cage, and Temporal Shunt).
Where: Range, Target & Area of Effect (AoE)
The spell's description will specify if the spell's effect is directed at one or more creatures or a place.
- Range: the spell may be restricted to the caster (self), touch (5ft), or up to a maximum distance away.
- Target: the spell may be directed at self, one or more creatures, one or more objects, or an area of some shape.
- Cover: unless the spell indicates otherwise, targets gain the benefit of cover if there is not a clear path between the caster and the target. Some spells require the target to be seen, which will fail against a target hidden or behind full cover.
- Point of Origin: When a spell effects an area, the shape of that area will be relative to a location where the magic effect begins. This may be the caster herself or a selected point within the spell's range, depending on the spell description.
- Cone: Extends outward growing from narrow to wide from the point of origin, up to the listed length.
- Cube: The described effect size is the length of each side of the cube with the point or origin on one side.
- Cylinder: The effect is in a radius around the point or origin, then either rises bottom to top or top to bottom from that radius.
- Line: Extends in a straight path starting at the point of origin to the listed length, as wide as described.
- Sphere: Extends outward from the point of origin in all directions. The spell description may clarify how the expanding effects interact with walls and obstructions (for example, Fireball wraps around corners, but is still limited to its radius).
When: Duration & Concentration
Duration tells us how long the spell effect will last. This can be in rounds, minutes, hours, days, or until something happens like it is dispelled. Many spells are simply Instantaneous, meaning the spell happens when finished casting and then is immediately finished after its effect has been applied.
Many spells with lasting durations require Concentration to keep its effect active up to the listed duration. The spell will end the moment the caster does not maintain Concentration:
- Any time, by caster's choice (no action or turn required).
- Being incapacitated (or a long rest) or being killed.
- Casting another spell that requires Concentration (you may only concentrate on one spell at a time).
- Using the READY Action with a spell requires both actually casting the spell (using the MP), and also Concentration while you hold it ready to release (even if the spell does not require concentration itself). The MP and Concentration happen even if you decide not to cast the spell.
- Taking damage while concentrating requires a check of CON vs. DC 10 (or half the damage taken, if higher than 10). This check must be made separately against each and every damaging attack.
How: VSM Components & Spellcasting Focus
The spell descriptions will list V, S, and/or M "components". If the caster is unable to supply all of these components at the time of casting, he is unable to cast the spell.
- 😮Verbal (V): VOICE Nearly all spells at least have a verbal component - some magical words or chant as sounds whose pitch and resonance weave the threads of magic. (If gagged or in a Silence'd area, the spell cannot be cast).
- 🖐🏽Somatic (S): HANDS Gestures might include tracing symbols in the air or directing energies - but requires at least one hand free (unless you have the War Caster feat or a similar aid).
- 🪶Material (M): THINGS The ingredients of a spell (a twig, ashes, copper wire, etc.) are listed if needed in the casting. These may be held within a component pouch (so specific objects need not be found), or replaced by a spellcasting focus. However, if the material component lists a COST, then that specific component cannot be replaced by a focus, and if the spell description says it is consumed, then that component must be purchased for each casting of the spell.
Casters may in some cases may use a Spellcasting Focus to replace material components - a wand, orb, scepter, staff, holy symbol, or similar. Warlocks and Wizards can use a variety of such items. Clerics and Paladins may use their holy symbol as a focus. Druids may use a sprig of mistletoe, yew scepter, nature totem of feathers/fur/bones/teeth, etc. Bards can employ a musical instrument as a focus.
What: Results vs. Attack Rolls & Saving Throws
After determining the casting time, the magical fuel, the range and area to be effected, the duration, and the needed components - the spell is cast and alters the weave of reality. The spell description will explain what happens next. Magical effects in general do not "stack" - the most powerful effect will replace (not add to) duplicate effects.
In many cases, an attack roll and/or a saving throw roll will be called for. A d20 determines if the spell "hits" (using the caster's "spellcasting bonus" added to the roll, like a weapon attack) or if the target(s) resist the spell effects (based upon a DC of 8 + caster's spellcasting bonus).
The spellcasting bonus is the caster's proficiency bonus + the caster's spellcasting ability modifier. (For example, a 1st level Wizard with a 16 Intelligence would have +2 (proficiency) +3 (INT modifier) = +5, and therefore a saving DC of 8 + 5 = 13).
Remember also with ranged attacks that you have disadvantage at a range of 5 feet or under if the creature can see you and is not incapacitated.
Listings of Spells
Note in this campaign spell descriptions will be based upon this source reference.