WoM

You have three things which you can run out of, and really don't want to:

Health, which is how much direct damage you can withstand before you're no longer able to do stuff. This is typically significant only in duels between casters.

Mana, necessary for most short-term magical spells, from cooling a glass of water to tossing a sphere of fire. Mana is replenished by the caster themselves, naturally, over time. Mana is regained quickly, but is of relatively little use beyond small-scale magic.

Essence, used primarily in spells of a grander scale, which is considerably harder to restore than mana. Essence is typically regained only through the territory one controls, and for the most part is utilized only in extremely powerful spells, or ones which are meant to affect a large area.

Disciplines

Arcane Necromancy Divination Artificing Alchemy Fire Water Air Nature Earth Summoning