The central conceit of the setting is still pending, but we're in luck. Anonymous Friend 2 has provided a description of the arcane casting system:
So it appears, it’s up to me to explain magic in this system … joy?.
So the first part I should mention is the fatigue system, since the spellcasting is supposed to avoid the 15minute adventuring days, but seems to result in most mages being basically hypersomniacs. So the fatigue track has various levels all of which are synonyms for being tired in some way, and give penalties of 0,-1,-3,-5 respectively, below that is unconscious, which is pretty self-explanatory, and further below that is Dead. Ok I can kind-of see the penalties for being tired being logical, and not needing 8hours of rest to recover from minor tiredness. It takes 5min of ‘rest’ to go from the -1 to the normal (0) state, takes 2hrs of sleep to get from -3 to -1, takes 4hrs of sleep to go from -5 to -3, and takes 4 hrs to go from unconcious to -5.
Every time you cast a spell you have to make a check to not fall on the fatigue track, the spell always succeeds, but for every 10 you fail by you drop another level on the fatigue track, which combined with fatigue penalties means at -3 or -5 most mages have a decent risk of falling unconscious or instadying from casting many of their spells. The spell scaling for the difficulty of these checks also makes it incredibly difficult to cast the higher level spells since the DC increases by +4p/ spell level, while if you sink a decent sum into increasing your casting stat (which you presumably should since it helps a lot of other things like will/toughness saves) it will only give you a +3 bonus every 2 levels, with a feat that adds +2. Making it basically a ~50% chance of dropping fatigue every time you try to cast your highest level spell (assuming not tired). Also since a nat 1 counts as rolling a -10, and nat 20s count as rolling a 30, getting a nat 1 guaruntees unless casting a spell ~4-5 levels lower than your highest you will drop on the track, and if it was a higher level spell it will drop you two (or three). Making casting higher level spells potentially literally suicidal, since 5% is only small when it only has minor penalties like not succeeding and not massive ones like your character dropping stone dead.
Many of the spells are based on the d20SRD spell but modified in some ways and often split into more spells and/or spell progressions. For example minor creation as a lvl 4 spell, creation (added) as a lvl 6 spell, and major creation as a lvl 8 spell, presumably with Uber creation as a lvl 10 spell. Often spell effects are basically an, ask your GM (for utility spells, or anything without damage effect etc.). I tend to make custom spells and some of those were interesting, effectively constructing elemental monsters under my control, I wasn’t going to complain, but in a balanced system infinite troops at low level is a recipe for disaster, luckily they were basically only used as shields to allow us to do harder dungeons with only 2 people.
And don’t get me started on metamagic, which was heavily altered, the only one I know still works is quicken, which reduces the action needed to cast a spell by 1 to a minimum of 1, but adds +4 to the DC. Luckily many of the NPCs are capable of handling a +12 to their DC and casting spells for 1 action (typically having 8+actions). When I have used the metamagic, even on theoretically easy spells, I always end up fatigued. So hypothetically an epic level caster can cast 10-12 epic level spells (lvl 10 spells) every round, and effectively be able to decimate entire fleets of massive space ships if I recall correctly.
There is also counterspelling, which is pretty much ‘blocking’ a spell, but much harder and costs 2 actions. To counter a spell you must first be aware of the spell being cast, once that is met you ‘cast’ a ‘spell’ of your own at a spell level of your choosing (see above for how that works) and make a caster level check with the level of the ‘spell’ chosen being added to the roll, against the person casting the spell/their spell DC, I honestly don’t remember, it was really never worth doing. Caster level checks basically work by adding the characters caster level to a d20 roll, while spell save DCs were calculated as 10+caster level + casting stat modifier (such as int for arcane and charisma for ‘Alternate casters’)+spell level (not counting metamagics I think), leading to the roll statistically always going to the original caster unless the counterspeller was much more powerful than them. And unlike melee combat, failing to block actually costs something (2 actions and fatigue risk as opposed to 1 action) so rarely an effective use of actions.
Also many spells weren’t deemed spell-like and so a ritual skill was invented, which I found fine, and it basically can be used to do things with enough ritual participants, but if anyone messes up, bad shit happens, and if the primary ritual leader or whatever its called messes up its catastrophically bad, which given nat 1s are -10 is almost always a risk until levels 10-12+ where simple rituals can be done without major risks since a nat 1 results in only failure not terribly bad failure.
Enchanting is also a skill, which allows someone to spend 8 hours shoving magic into an item to give it a magical effect, suffice to say this leads to interesting results, the DCs are too high for any low levels to produce enough magic items, if any, to destabilize the campaign, unless one of them has a thuribibile (I can’t spell or pronounce that), the only reason I was able to make any magic items is because we found an enchanting artifact and basically claimed it as mine, allowing me to pump out moderately powerful magic items, unfortunately this caused the DCs to be balanced to a character having an effective +20 added bonus on top of max ranks a high related score and a focus skill feat into it, whoops?. So now it is impossible to make a +4 item equivalent without being nearly epic level, or having basically a ton of circumstantial modifiers.