If I've missed a part in the rule book that addresses this, then please let me know what page to look on.

So, how would you all handle underwater magic? Do spells still work the same? How does fire work underwater? Electricity?

Magic in Genesys generally doesn't have a fixed special effect. So mostly you just apply cinimatic logic. There are casting penalties that may apply if you cannot incant, gesture, or concentrate due to being underwater. These might be negated with an appropriate narrative barrier spell (such as an Air-Bubble Charm)

In Harry Potter (book 4), a simple 'firework' attack spell created a damaging stream of scalding water instead. Mechanically it worked much the same as the open-air version, the described special effect simply changed to match the environment. If Harry Potter had 'failed to cast the spell' (in Genesys terms) Rowling (as GM) could have written that he chose a spell that didn't have an underwater permutation, or flubbed up the gesture.

Assuming we're talking about the generic magic presented in the GCRB and RoT: If a PC is explicitly casting an "open-flame-generating spell", such as because "Fireball" is their Signature Spell, I would be inclined to upgrade the Difficulty once or twice (per the table in GCRB 210), and interprete the results appropriately. This may mean that the spell more or less "works normally" and the description given simply changes to justify the results. For example, I might describe that the caster remembered they knew a simple spell to boil water, so they just mashed the incantations together and hoped for the best. If they cast such a spell regularly I would eventually stop imposing the penalty; to represent that they had created a viable "Underwater Fireball" spell.

Otherwise I would have to rule that the check is simply Impossible (per GCRB 18), and it would automatically fail (wasting their action and the strain spent). However that feels unfun, and like punishing the PC for using their talents.

However if we're talking about a more structured magic system than Genesys defaults to; as is fairly common in cinima and literature. A pyromancer or fire-bender may be all but powerless underwater if their abilities rely on generating open flames instead of just heat. If so, that should be noted in the skill's description as an additional difficulty modifier alongside any other unique rules. If such a limitation is likely to be common, give the skill a compensating benefit. For example:

Fire-Bending might be dampened by water (upgrading the difficulty of fire-bending spells twice if the caster is drenched or underwater), grant very few actions (maybe even just Attack and Utility spells), and cannot benefit from Magic Implements... but in return it's spells may only cost 1 strain, you can apply the Close-Combat effect to them for free, and Ranks in Fire-Bending might count as ranks in Knowledge for the purposes of thematically appropriate Attack Magic Additional Effects (such as Blast, Fire, and Lightning).

Scalding hot water.

*slaps forehead*

I never would've thought of that.

Electricity is harder to justify. Narratively, the key is that the spell needs to create a difference of potential energy between the target(s) and the caster, and a conductive surface for electrons to flow along. A "lightning bolt" is simply a stream of plasma connecting areas of differing potential energy (such as the caster to a unsuspecting goblin).

Being submerged in water can electrically insulate you, making it impossible to target you with such spells unless the caster can create a connecting surface for the electrical energy to flow along (which is how an air-taser works).

Conversely, a set of targets being in contact with water (but not submerged) might automatically trigger an electrical attack's Blast quality (or grant it an appropriate Blast quality), just like being in a small room with a live grenade.

remember 2 setback for being unable to speak

On a more serious note there is no need for it to be actual electricity.

The additional effects are just words and mechanics but they could look how ever you want. Nothings dictates that lightning is actual lightning or fire is actual fire. So it could be anything really that fits the story. If your in a underwater world your mage could be sprouting tentacles like lightning eels that bites the opponent or scalding water like suggested. They only thing those effect do mechanically is add stun damage and potentially auto fire or in case of fire burn quality. How that looks if it be lighting or 1000s of tiny darts docent really matter.

1 hour ago, Archellus said:

The  additional  effects are just words and mechanics but they could look how ever you want    . 

That too, but I was assuming the OP was refering to actual incendiary and electrical spells such as Burning Hands, Shocking Grasp, Fireball, and Lightning Bolt. As opposed to the Fire and Lightning Magic Attack Additional Effects, which are simply examples of possible side effects, given evocative names for the sake of usability.

Yeah, my goal is to be a cinematic GM. Don't let the rules get in the way of a good story.

I was wondering how things like fireball and lightning bolt could work underwater. I am running the Pathfinder AP Ruins of Azlant and they are about to hit the first of many many many underwater parts.

Ice and *snicker* water are easy enough. Wind you can figure out. Fire makes sense when you frame it as scalding hot water. Electricity is the real hangup. Well, electricity at a distance.

*thinks about it*

Would it be as simple as saying the electricity is wrapped in an "air bubble" as it makes its way to the target?

Well it is magic, so as long as it sounds good it doesn't have to be scientifically accurate.

Your spell could cause an electrical discharge inside the target (basically like a nerve misfiring but more severe). Alternatively the spell might launch an electrically charged projectile that discharges on impact (much like an air taser, but with a magically conjured medium and power source).