Right-o, magic. We'll get to the overpowered-ness of sword schools after this.
Some fluff bits, although "There are many that believe sorcerers represent a gross perversion of the natural order, and a constant reminder of the terrible powers of the warp. This idea has led to sorcerers often being kept tightly under control, with most races having a government-controlled organization in place to control and train those with magical ability." Which is useful to keep in mind. There's a bit about types of sorcerers, astropaths, sanctioned, navigators, apostates, and untouchables. However there is also zero implementation of these types in the game, aside from the existence of the tested feat. So I'm forced to assume that this is pretty much more fluff/setting/ideas than anything else. A "magical ability" section talks about five trails to get tested. Nice if you want to roleplay through taking the tested feat (take it and rp or get is as a reward for a rather arduous rp arc, either/or).
Then the actual casting of spells. Getting a warp phenomena doesn't mean that you casting has failed (often the opposite actually). Three ways of casting a spell, fettered, unfettered, and pushing it. Fettered you get half your normal number of rolled dice (which can reduce the number of kept dice some times) but you can't invoke the perils of the warp. Can't is can't, this is the safe caster option. Unfettered is rolling normally. Pushing it automatically invokes the perils of the warp but you get extra dice rolled. sanctioned/tested casters get up to 3 more dice, unsanctioned get up to four more dice. This does mean that your effective magic school rating can go 6 or higher but it notes that if you have more than one source of increases to you magic school rating that only the highest one applies.
Fettered casting, half the rolled dice (and of course no more kept dice than rolled dice) and no warp effects. Its not too hard to start with 6k5 (daemonhost/atlantean for magic 1 & getting the casting stat to 5 OR vamp/were at stat 4 and using necromancy or transmutation) which would drop to 3k3 which puts you at about a 66% success rate for your first level DC 15 spell.
Unfettered casting, roll normally. Normally is magic school + stat, keep stat. If you get any 10s you have a choice to make. Ditch the exploding die and possibly not make the cast, or keep the exploding die. If you keep one die you may as well keep them all. Sanctioned/tested sorcerers roll on the psychic phenomena table if they keep an exploded die. Unsanctioned, without the tested feat, you roll on the table at +5 per level of the spell.
Pushing your casting means that you just flat out roll on the table while casting. Sanctioned roll at +5 per additional die, maxxed at 3 dice for +15. Unsanctioned roll at +10 per die, maxxed at 4 dice.
So this is interesting, it's one of the places that my group has been doing wrong. Well, wrong-ish. We've done +5/+10 per kept exploding die on regular casting and +5/+10 per pushed die AND +5/+10 per kept explosion. So our costing has been significantly more dangerous as a 4 die push with 3 kept 10s results in a +70 on the warp effects roll. Now there's two d100 tables, psychic phenomena and perils of the warp, in the book. You roll with whatever modifier you have on the phenomena table and if you roll 75+ you roll on the second table. For the longest time (actually we kinda still do) we applied the same modifier to the second table, the perils of the warp. It's the perils of the warp table that has the nasty stuff on it. The phenomena table tops out at 1d5 hit points of damage, a point of insanity, testing versus fear 2 (willpower vs. 20), being thrown 1d10 meters into the air, or frying nearby electronics and jamming weapons. The perils table has such light-hearted effects as everyone within 3d10 meters swapping places with random other people, or not being able to cast for an hour. Those are the safest effects, double ought is just straight up sucked into the warp and destroyed. So naturally +70 was pretty much instant death when run that way. We've also run it as casting doesn't provoke attacks of opportunity, which it should. I should note that the guy at our table who was the main caster 1) freaking loved the warp effects, and 2) never read any of the magic stuff except certain parts of the spells. This was evident when he finally told me, after his character hit 100 insanity and got turned into a table (long story), that he'd told me his kept exploded dice were one per 10 on ANY die he'd rolled and kept. Thus a roll where he'd had two 20+ dice he'd told me had 4 exploded dice for a +40 instead of a +20.
So. Officially. Unfettered keeping exploded dice is a +0 roll for warp crap if tested, +5/spell level if untested. Pushing is +5/extra die if tested, +10/extra die if untested. Which means that an untested caster pushing a spell by a single die is 'safer' if the spell is 3rd level or higher if you're expecting to keep exploded dice.
For our game I've written a warp effects roller. Because enough rolls on the tables in the books was getting repetitive (25 and 18 entries). This roller and the associated tables was built on the assumption that you were adding the +# per exploded die and/or +# per pushed die AND +# per exploded die. There are 4 tables in increasing severity. The first has 50 entries, with one being roll twice (second roll at no modifier) and another being roll on the next table with -10 on the modifier (minimum +0). The second table is slightly more dangerous than the first but has the same number of entries and the same last two lines. The third table only have 37 entries, same last two again. The last, and the only table with actual flat-out death on it, has 35 entries of which 3 are actual instant death, one is the roll twice, and 6 are "Roll 1d10. If the roll is less than 8 roll twice on the preceding table, on 8 to 10:" with the 8 to 10 roll being hideous, gorey, spaltter-punk, instant death with side effects. Since everything is percentiles and you need three 99+ rolls with a -10 on future rolls you need to have rolled quite high several times in a row just to get onto the instant death table. Actually, let me do the math now... on a +0 roll there's a 0.0009% change to get to the instant death table versus 0.25% of instant death by the book... and I'm definitely making mistakes on trying that at +20 so I'm probably making some mistakes on the +0 one as well. Eh, it's late. Suffice it to say that the multi-table roller is overall less instantly deadly and has more variety.
Details, details. Stuff from multiple spells don't stack, only the highest applies. You need line of sight or to otherwise be aware of the target as well as to be in range, invisibility won't save you if they can see your footsteps. Anyone with casting ability can make an arcana + wisdom vs. 20 to detect magic and determine the source. When you gain a dot of a magic school you learn a spell of that level or lower, you need the spell book feat to learn more spells than that. There's no trading out spells, your choices are permanent.
How to read the spells. There's an editing error, in the focus power test text it mentions rolling doubles invoking perils of the warp. Since that isn't repeated anywhere else (and would make casting quite risky and nasty) I'm sure it's an editing mistake from an earlier draft of the rules.
Keywords for the spells. Important subtleties on how a spell works. Attack. Combo-OK -usable in spell combos. Focus - requires a material focus to cast and maintain the spell. Language dependent. Material - has a consumed material component. Mind affecting. Ranged touch - requires a ranged attack, I don't know of it's a typo or not that it says dexterity + ballistics instead of level + ballistics. Saving throw - allows a save, people who saves know a spell tried to affect them even if it's subtle, the DC of the save is either listed in the spell or is the result of the focus power test used to cast the spell. Social - cannot be used in combat (actually important, I'd misread this one and thought it was more of a 'socially acceptable to cast' sort of thing). Somatic. Verbal. Subtle - casting and effects aren't immediately obvious, other casters can try arcana + wisdom to notice it. Touch - requires a normal level + brawling test to tag someone.
Duration, the time can be real units like days and minutes or game units like rounds and scenes. If it's concentration the description will include what sort of action is needed to maintain the spell (it's usually a reaction, so it would eat your reaction each turn to maintain concentration). No mention of being hit or damaged breaking your concentration so I presume it doesn't. An "(E)" indicates the spell can be expended, details in the spell's description.
Spell combos, spend xp to combo two spells that you know into one, cannot be done during character creation. Takes 50xp per level per spell in the combo to create it. DMs don't have to allow combos even f you have the xp. Use the lowest characteristics and the lowest magic school you have in the combo for casting it. DC to cast is the highest one of the spells in the combo +5 per additional spell. Cannot be cast fettered, and warp rolls are at +5 per spell in the combo in addition to whatever else is going on. Takes an action to cast equal to the longest casting action, no speeding anything up here. Focus, material, and VSM are combined and missing any means you fail to cast. Unless every spell in the combo is subtle the combo isn't subtle. Everything else, is tracked separately for each spell in the combo, range, duration, attack rolls, saves, language dependency, mind affecting, etc. Can't use the same spell twice, so no double fireballs.
I think that one I did for an Athasian sorcerer-king was something like blink + luck + energy grasp. Blink, TN 15 conjuration + willpower, 1/2 action somatic instant, to teleport 40m. Luck, TN 20 divination + wisdom, 1/2 action subtle scene expendable, to get extra rolled 'luck' dice to stuff. Energy grasp, TN 20 evocation + charisma, 1/2 action touch attack verbal & somatic, brawl attack with evocation + charisma for the damage roll. So that was 250xp (a first level spell plus two second level spells) for a DC 30 casting check that used the lowest of conj/div/evok + will/wis/cha. Mind, as a high end sorcerer-king he was still throwing 8k4r1 at that, defiling (Athas overcasting) for four extra dice putting him at 10k5r1 casting. I think he got a bit below average, about 45 or so. Which gave him 4 luck dice, a 40m line of sight teleport, and a (this is where you use those luck dice) brawling attack for 9k6 magic (ignores armor) energy damage. He used it to blink into the cockpit of an assault shuttle, the target dodged so a bulkhead got a meter+ wide hole blown in it from the punch. The 45-50 damage that attack usually puts out is going to harsh up just about anyone.
Ok, that's the magic rules. I'll start in on the spells next.