Every piece of magic in the game obeys one law:
I = W / (r + R)
You supply a potential W and your own resistance
r; the effect you are driving is a load R. The
current I that results is the one shared quantity all magic
trades in. What the world sees is I²R — the work done in the
load. What you feel is I²r — the heat that stays in you.
Casting is a rhythm
You never pick a magnitude from a menu. Hold the channel and tap to the effect's resonance: your first tap sets the beat, and every later tap is scored against it. A kept beat feeds the cast; an off-beat tap brakes it as hard as a kept one feeds. Mashing cannot beat keeping the beat — one beat, one credit.
Vigour is the mana
There is no separate mana pool. Casting spends the same vigour that
sprinting does, and a drained body casts worse: your resistance is
r = r_skill + r_fatigue(vigour), so the wizard who ran to the
fight arrives a worse wizard. Chain-casting throttles itself — each cast
raises your fatigue, which makes the next cast less efficient.
Power transfer, and why masters are precise
The most power moves into an effect when its load matches your
resistance, R = r. A novice's matched load is a big, gross
effect; a master's is a small, subtle one that carries far more power.
Getting better does not make you a bigger hammer — it makes you a finer
instrument.
The short circuit
Drive hard into a tiny load and the current runs away. An archmage who kindles a candle at full drive can detonate it and cook their own hands. The skill the game is testing is throttling, and the burst guard gives even the fastest hands only a few seconds of margin.
Glyphs and foci
A glyph is a pre-formed circuit — the shape of an effect. Everybody knows light; the rest are learned by being taught, and each one you learn earns a page in your encyclopedia. A focus such as a staff sits in series with the cast: it always adds resistance, but a staff tuned to a glyph's resonance adds far less than bare hands mismatched to it. A mismatched focus is worse than holding nothing.