If you haven't already read my first impressions of magic in Genesys, I recommend doing so for some context. In short, I'm not happy with the magic rules of Genesys because the drawbacks are too harsh for what you get. I think it might be instructive to convert some basic D&D spells to Genesys to showcase exactly how the extra effects adjust difficulty, and what you're getting for your trouble.
I'll be a little more generous to the magic users this time, and assume that they have a 4 in their relevant spellcasting characteristic. In the years I've been playing Star Wars, I've personally only created a couple of characters that started with a 4. I'd much rather have 3 in half of my characteristics, but that's personal preference and I tend to enjoy well rounded characters more. But mages need all the help they can get, and a 4 will help achieve that.
Also, I'll assume that the magic user is using a Staff, for simplicity. You can game the system a little bit by swapping out implements to suit your spell, but since the same is true for weapon users (everyone will ultimately be limited by how much gold they have) I don't consider it an inherent advantage of mages.
To start with, a classic. Arguably the most iconic D&D spell. You're obviously going to use the Attack spell, and we're going to add Fire to it (duh) for +1 purple. I'll also add Blast for another +1 purple, even though Blast sucks and probably isn't worth using. The problem is, you can't really have a fireball without Blast, so the fact that it sucks just shows that Genesys doesn't do a great job at replicating fireball. Finally, I think we need to add +2 purple dice for Empowered. Fireball is about damage, and it's about a BIG blast. A blast that only hits things engaged with the target isn't really Fireball, it's more like a puny little Scorching Burst.
Fireball winds up being a 5 Purple check (Formidable). It's worth mentioning that even high level Star Wars characters rarely have to make a Formidable check. Thanks to the Staff, we can cast Fireball at medium range for free. In D&D it's typically a longer-ranged spell, but I don't think adding a 6th purple die to the difficulty is remotely worth it. You could also argue that since Fireball targets Reflex (or, in Dungeon World, ignores Armor) that it might be worthwhile to add Destructive to it. But that's another +2 purple and no character can really handle that. It's not as integral to the spell as Fire, Blast, and Empowered.
You end up with Base Damage of 12, Medium Range, no crit rating, Blast (probably 2-4, depending on ranks in Knowledge), and Burn (2-4). Keep in mind that Blast and Burn both require 2 Advantage each to activate.
For fun, I'm going to do some test rolls to see how our hypothetical, Fireball flinging Wizard fares. Two ranks in Arcana are assumed. I'll assume the main target has Adversary 1. Our dice pool is thus YYGG RPPPP.
Roll 1: 1 Failure, 3 Advantage. We can activate Blast! It will probably only be 2 or 3 damage though, and only the the primary target. An Adversary 1 enemy probably has more soak than that.
Roll 2: 1 Success, 3 Threat, and 1 Triumph. 13 damage isn't too shabby, and with the Triumph we'll activate Burn or Blast (Burn is better). In a couple of rounds, our primary target is probably toast. But with 3 Threat, the GM can decide that an ally was caught in the Fireball, too! 13 damage to a friend. Ooops. Or the GM can be a real dick and cause the Wizard to lose 6 more Strain (on top of the 2 spent to cast the spell), or take 3 Wounds (maybe the Wizard got a little singed).
Roll 3: 1 Failure, 0 net Advantage/Threat, 1 Despair. Cool, Mr. Wizard just spent 2 strain to either fry a friend (and just a friend), or become unable to cast spells for the rest of the encounter. Great.
Roll 4: 2 Failure, 0 net Advantage/Threat, 1 Triumph. Well, I guess we're triggering Blast again, but unless the enemy is a glass cannon we won't penetrate soak. Better to come up with something creative.
Roll 5: 2 Success, 3 Threat, 2 Triumph. Holy dice luck, Batman! This is probably the best we could have hoped for! Those 3 Threat are REALLY nasty, though. Ok, so you hit the primary target for 14 damage, and we're DEFINITELY going to Burn that guy. He probably won't last another 2 rounds, even if everyone else ignores him. And we're going to Blast everyone else (but for a measly 4-5 damage). Depending on your enemies, the Blast might ACTUALLY do something! But keep in mind that Stormtrooper equivalent mooks will have 5 soak. Let's mix it up and spend 1 of those Threats to deal 2 Strain (for a total of 4 this turn), and then we can either crack Mr. Wizard's Staff, or say the Fireball takes an extra round to go off. Neither option is particularly appealing, but it's worth mentioning that the GM can be a REAL dick here and if the blast is delayed, have the mooks clear short range so Blast does nothing.
So out of 5 rolls, 3 were failures. One of the failures was tempered with Advantage and one with Triumph, but nothing inherent about the Fireball could be triggered to useful effect (shame about Blast sucking). Just come up with something cool and creative. One of those failures had a Despair, and what a garbage roll it was. Adversary is a dangerous thing (so are Story Points). Of the 2 successful rolls, one was actually pretty awesome! The other wasn't terrible, but that nastier Threat/Despair table reared its ugly head, and proved to be one cost too steep for magic users.
I won't do sample rolls for every spell, because I think I've made my point. You end up failing a lot, despite the fact that you had to spend 2 Strain to cast the dumb spell, and hopefully you didn't make 2 maneuvers that round for a grand total of 4 Strain (before Threat) to do nothing. Also because of the large number of negative dice in your pool, you end up getting a lot of Threat! Which is worse for mages. And along those same lines, you DON'T generate much Advantage (so good luck recovering Strain from your rolls). I did roll a lot of Triumphs, which is great, but it would be even better if Blast were more useful.
Ok, I used this example in my last post. I'll be quick. You use the Curse spell (one of those pesky 2 purple base effects) and add Paralyzed for +3 purple. It's a good thing we can already cast at Medium range with the Staff, because we can't really afford to add anything else to the spell (nor do we really need to).
This is a 5 purple check, and for 1 turn the target loses 1 point from one of their Characteristics and can't take actions. It's in your best interest to spend several turns Concentrating (even if you have to pop strain for a second maneuver) to keep this effect sustained!
Ultimately, if you're trading your turn to make an enemy lose theirs, the enemy should be stronger than you for it to be worthwhile. Expect at least a couple ranks of Adversary if you're using this strategically.
The only spell that can make this work is Augment. You want to be a bear? I know you do! The base effect is 2 purples, and we're going to use it to increase our Brawn. Probably from 2 to 3, or maybe we built a Druid focused on combat shapeshifting, in which case we're going from 3 to 4 Brawn. Magic isn't necessarily reliant on just 1 super stat.
Primal Fury is the obligatory add-on to this, for +1 purple. You get a halfway decent crit rating (3), and can add damage to unarmed attacks equal to your ranks in Knowledge (2-4 probably, we'll use 3 as our average). I honestly wouldn't both adding any other effects to this, to keep it at a hard (3 purple) check. But think to yourself, are the enemies you're engaged with likely to try to run from you, or face you head on? Haste might be worthwhile if you think they'll run, because you're going to be spending a maneuver Concentrating to maintain your form each turn. You'll burn through a lot of Strain if you have to chase people down. If there are nasty terrain effects in place, you might also want to consider Swift, and fluff it as the bear just powering through everything. But again, these are situational. Are the benefits worth adding more purple dice, and possibly failing the check? You're already spending 1 turn just casting the spell even if you succeed, while Mr. Greataxe Guy can wade right in. I'd suggest that if you roll 1 or 2 Triumphs (depending on how generous your GM is) saying that you cast the spell quick enough to go maul stuff this turn. Also, if you're planning on playing a Druid who specializes in shapeshifting, you should probably create a custom implement that lets you not have to Concentrate every turn. You could even tweak the Druidic Circlet to support Augment instead of Conjure.
What you end up with is a 3 purple check that lets you be a bear, so next turn you can use your claws to deal Brawl damage that's worth a damn. With the upgraded 4 Brawn that's 7 base damage (with Knowledge 3), and you should probably make sure you have ranks is Brawl in order to get yellow dice when you do this. You can crit with 3 Advantage, and don't forget that Brawl attacks have Knockdown by default! Flavorful for a bear, too!
Augment works ok for Wild Shape. It can pretty easily replicate turning into a wolf or a bear, but what if you want to do the cool, creative stuff with Wild Shape? You know, turning into a hawk to be able to fly, or an octopus so you can latch onto someone's face in the middle of combat and ink the crap out of them, or something like a crocodile or panther that is useful in combat, but also has some utility (can swim or climb well). I guess you can use Swift as a baseline to get swim or climb speed. And flight is probably not going to be a combat form anyways, so go with the suggested Hard difficulty for flight or invisibility in the base description. Not sure about that octopus thing, though. I did that in Dungeon World and it was REALLY cool, but at best if I tried it in Genesys it would stall the game as the player and GM try to figure out how to represent it.
Overall, it's a strain-heavy way to turn yourself into a brawler, that costs you a turn. Tough to say if it's actually worth it, but I would say that if the player were really creative about narrating Advantage/Triumph rolled while fighting in animal form, it could be a lot of fun. And Threat could be a cool way of having inconvenient animal instincts kick in. I'm cautiously neutral on whether Genesys could make a Druid both fun and effective.
Fireball's cousin. It was VERY similar to Fireball in D&D (blast vs a line), but in Genesys it'll work pretty differently. Attack is our spell, obviously. Let's keep this simple and just add Lightning to the basic attack for +1 purple. If you really need to, you can add another +1 purple to bump the range out, or I can even see someone wanting to add Deadly, Impact, and/or Destructive to emulate some possible consequences of getting hit by lightning. I'd recommend against Destructive since it's +2 more purple.
Our difficulty is actually a little deceptive here, because Lightning gets us Autofire. If you're not going to use it, you might as well not even be adding the Lightning quality, so right off the bat the difficulty gets increased by 1. That brings us up to a hard (3 purple) check to cast this thing at Medium range. That's actually not too shabby.
Base damage is 8. We didn't take Empowered like we did with Fireball, because we don't care about Blast, and the extra 4 damage probably isn't worth making this a 5 purple check. Remember how many sample rolls failed for Fireball? Anyways, 8 damage, no crit, medium range, Autofire, and Stun 3 (for our assumed average 3 ranks in Knowledge).
Pro tip - unless you're fighting a mage who is also burning through Strain (just like you!), don't bother using Stun. Actually, even then it's probably not worth it. Why? Because it costs you two Advantage to use. And if you have two Advantage, you should be triggering the extra hit from Autofire. Which can trigger multiple times. Assuming you have enough Advantage for it.
Here's the rub. Compare Lightning Bolt to an Assault Rifle from the Modern setting. Same base damage of 8, but it crits on a 3, goes out to long range, and only has Autofire, no Stun. But we already decided Stun wasn't worth triggering when you have Autofire. Ok, so technically it MIGHT be worthwhile if your opponent has 8 or 9 soak, but that probably won't be the case. The Assault Rifle is better (because of its crit and long range) and doesn't cost strain to use! Interestingly, the difficulty in this example is the same (3 purples at medium range, both can opt to add a purple to shoot at long range).
I guess if you're playing fantasy it might be tougher to find weapons with Autofire, but you'll also probably have more melee guys getting up in your face (requiring you to add a purple for close combat or spending a maneuver to disengage), and magic weapons tend to go along with fantasy settings. The only magic item in the core book is plate armor, but I'm sure we'll get magic weapons in future splatbooks, and GMs can probably make them pretty easily. Point being, one of the tropes of fantasy is that the basic equipment isn't what you're going to stick with, so I can imagine bows or even melee weapons being enchanted with Haste spells to gain Autofire.
Cone of Cold / Ray of Frost
Hmm, I realized after typing "Cone of Cold" that the Attack spell doesn't have an option for multiple targets. You have to make due with Blast or Lightning, or if you're really into the idea of multi-target/AoE spells you can just use an Orb instead of a Staff. Although it's unclear if the orb allows you to affect multiple targets when it's not on your list of additional effects. Basically, talk to your GM to see if they'll allow it.
Ray of Frost really just needs Ice, and potentially Ranged. The whole point is to get melee fighters stuck away from anyone they can attack. You can do that pretty easily with a 2 purple check (or 3 for long range), if you're willing to deal only 8 damage, not have a crit rating, etc. But this seems like a great way to hold off a melee guy. Technically, even if they have a ranged weapon they can't draw it, because Ensnare prevents you from using maneuvers. They'll waste at least one turn trying to break free of the ice with an Athletics check. You can also use this on ranged guys to get them stuck next to your melee friends.
Ray of Frost functions similarly to Hold Person, but the difficulty is so much lower. Sure, it's a little more situational and takes a little more thought to use, but I'd say it's worth it to have a lower difficulty. There's really no reason for these two effects to have such a large difficulty differential.
As a bonus, I'll suggest another ice themed spell. Something called Blizzard, Icy Wind, Icy Terrain, or something. Basically, you can add the Manipulative effect onto your spell for +1 purple and, if you get enough Advantage, you can move your target before freezing them in place! That's really awesome for when they're already engaged with your ally, but your ally is hurt and just can't stand to take another hit. You could theoretically also add Close Combat for +1 purple and push targets engaged with you away before freezing, but it's probably not a good idea. It's a cool concept, but Close Combat is another one of those effects that's probably not worth it. Better to just spend a maneuver to move away instead of adding a purple die into your pool. It is, however, situationally useful for those times when you, yourself, are Ensnared. Or maybe you just have other things to do with your maneuvers.