Magic is the exciting lifeblood of any fantasy story and Gestalt is no exception. Adventurers call upon the powers of the mana within their body and from the divine tempest itself to cause miraculous effects to happen. Anything from a fireball to levitation and even resurrecting the dead are possible with magic.
Casting a spell has a visual aspect (a sigil) unless otherwise noted. There is some degree of physical effort (hand movements, arm movements, etc) required to cast spells as well (though you may do so while wielding items).
When magic is cast it is traditionally accompanied by a sigil that appears in the air. This sigil looks distinct and reflects what spell is being cast, the school of magic it is (a divine teleport spell and an arcane one would look different), and who is casting it (almost like it is “signed” by the spellcaster). Sigils also change appearance when modified by metamagic or cast with more or less power (higher or lower levels of Spellcasting proficiency); generally speaking, stronger spells create more sigils. A sigil can be “read” (with an Arcane Lore check made to identify the spell) by skilled spellcasters. While they do “glow” they don’t glow enough to shed light. When a particularly powerful spell is cast energy is often discharged; a spellcaster can effortlessly suppress this but doesn’t often as a matter of pride.
Mana is the magical academic term for the base unit of magical power like a “gram” or “watt”. All spells cost 1 mana to cast unless otherwise noted. All mana is recovered after a long rest.
If you have mana from different sources, such as 2 different spellcasting classes, each source uses its own pool. You cannot, for example, use mana from your “cleric” pool to cast wizard spells, and vice versa.
You may cast a spell if you are a member of a class with the spellcasting keyword. Casting a spell typically takes 2 actions (unless otherwise noted) and provokes an attack of opportunity.
You can cast any spell you know and what spells you know is defined by your class’s spellcasting class feature. Spellcasting classes grant “mana”, and it costs 1 mana to cast a spell unless otherwise noted. All mana is recovered after a long rest.
Certain spells have requirements, typically needing you to be of a certain character level or higher to cast. Other spells get stronger when you cast them at a certain character level or higher.
When casting a spell you do not need to roll any dice to do so, though the effects of the spell might have you roll dice. Any dice roll related to casting a spell uses your Spellcasting proficiency unless otherwise noted.
You can take 1 action to prematurely end an ongoing spell’s effect that you cast. You must be able to draw light of sight and line of effect to the ongoing magical effect to do so.
Like a boulder rolling down a hill, once started magic is difficult to stop or interrupt. A spell cannot be interrupted or made to fail unless something expressly says it does. The only thing that stops a spell mid-casting is if the caster cannot continue to take the actions required to cast the spell before completing it.
A cantrip is a simple spell that costs 0 mana to cast.
Sometimes a creature replicates the effect of a spell by means other than casting a spell. An innate spell can represent something outside the formal definition of “magic” or “spells” (a more supernatural or even strange biological effect).
Innate spells do not rely on the creature’s Spellcasting proficiency but instead the most relevant skill or proficiency they have. The most relevant skill is sometimes suggested in a parenthetical. Use this proficiency to determine the DC of the innate spell, and you can use the skill in place of Spellcasting if the spell allows you to roll Spellcasting for particular effects (such as Dispel Magic).
Innate spells do not require mana to cast, and having one doesn’t grant you mana. They expressly do not work with abilities that require the expenditure of mana.
There are primarily 5 types of magic in Gestalt: arcane, divine, nature, psychic, and weird, with arcane and divine being the most commonly encountered. Magic interacts with each other without issue; the division of magic is in its origin rather than its effect.
As a reminder, if your character has 2 spellcasting character classes and they are reliant on two different ability scores you will have two different DCs. For example: if you are a wizard-cleric you will have a DC for your wizard spells based on your Intelligence and your cleric spells will have a DC based on your Wisdom.
Sometimes a spell will require a skill check (rather than a Spellcasting check). What skill that is depends on your school of magic.
A character who casts divine spells draws their power from a patron or belief in an ideal drawn from the divine tempest. You can’t cast divine spells without the implicit approval of the one granting you their power or against the ideals you hold strongly. If it goes against your patrons best interest or violates a tenant of your belief (often an oath) the divine spell will fail.
Examples: Trying to cast a divine spell that inflicts great suffering with divine energies from the healing domain will probably fail. Likewise, trying to turn the divine power of a demon lord against itself (or their minions) would fail.