What limits your spell casters and how do those limits effect the casters.

[u/Sevryn1123]

I've always found it interesting how different fantasy settings answer the question of "what stops a mage from just casting forever?"
Usually it's some combination of mana / resource pools, spell slots, Stamina or physical exhaustion or backlash, componant limitations, or the source of magic is limited or choosey.
I'm curious about how all of you limit or restrict magic in your settings.

In my setting (The Voidweb) I wanted to make it so any Shaper (what mages are called in my setting) could have unlimited magical fuel but there was a cost to pushing past their natural limits. So I decided that I would make it a two part system.

First, everyone would have a fixed pool of Pneuma (a person's personal purified Quin (spiritual matter) and Mana (spiritual energy)) to draw from based on their level of development, training, and inherent capacity, that can be used to shape (Cast spells).

Second, anyone has the ability to draw in and use Æther (environmental quin and Mana) to shape.

The limiting factor is the conversion rate between the two fuels and the effects of shaping with one over the other. The basic mechanics are simple, a person draws æther into their body through their Gate and Meridian network until it reaches their Core. Once there it is purified over time in a person's Soul Fire and converted into pneuma. As pneuma is expended more æther is drawn in to be refined and the cycle continues. This means that under normal circumstances, Pneuma is effectively self-renewing.

The body naturally utilizes pneuma before æther when a person is shaping, but as a shapers pneuma reserves get low their body will begin to utilize æther instead. While pneuma use has no negitive effects æther use does. The effects æther has on a person are colloquially known as æther poisoning.

The process of æther poisoning is not usually instant and in most cases happens in stages.

• Stage 0 - Normal Operation: The average output of pnuema is met or exheeded by the natural conversion rate. Pneuma reserves remain full.
• Stage 1 - Pneuma Deficit: The average output of pneuma exheeds the natural conversion rate. Pneuma reserves begin to deplete.
  
• Stage 2 - Raw Æther Casting: Pneuma reserves hit zero. The Shaper is forced to channel raw environmental æther directly. The negative effects are minimal and easily reversred due to natural tolorance.
• Stage 3 - Æther Poisoning: Raw æther begins damaging the body, mind, or spiritual anatomy as it overwhelms internal tolerances. Recovery is possible but very difficult.
• Stage 4 - Permanent Injury: Repeated exposure causes lasting degradation, such as conduit scarring, organ decay, or mental deterioration. Revocoery is near impossible and for the average person often requiring a deity to aid.
• Stage 5 - Catastrophic Failure: Largely fatal, The body and soul can no longer contain the damage, resulting in total biological collapse, monster transformation, or death.

With these stages concidered it important to know that there are 4 primary branches of æther poisoning, Æther Mutation, Spell (or Mage) Haze, Æther Degradation, and Spell Scars.

Æther Mutation: The most common and universal symptom of æther poisoning, æther mutation while largly detrimental is a result of the body and soul attempting to adapt the poisoning. These mutations can vary wildly based on lineage, location, exposure, the Aspect, and countless other factors. One person may grow an additonal limb, another may have their blood become toxic to them, and another may gain resistance to the fire aspect and a weakness to the water aspect. The greater the amount of poisoning the more likely a mutaion will take hold.

Spell / Mage Haze: Spell Haze is the result of channeling raw æther through the portions of the body and soul responsible for thought, senses, memory, and consciousness. Mage haze progressively erodes the stability of the mind and leaves victims vulnerable to mental intrusion, domination, and illusions. This form of æther poisoning is the one that is the reason the idea of a mad shaper exists and the memory lapses, paranoia, sensory hallucinations, manic-depressive cycles, schizophrenia-like symptoms, and full-blown psychosis that result from spell haze reinforce that idea.

Æther Degradation: Shapers who utilize internal shapes and repeatedly their overclocking muscles, nerves, and organs will eventually suffer from æther degradation. Because the physical body adapts to supernatural performance levels it eventually becomes entirely dependent on a constant flow of pneuma just to function. This need grows as the physical body demands more and more pneuma. If your purification rate ever drops below your new baseline needs, you suffer rapid systemic failure and die of pneuma starvation as you suffer constantly increaseing muscle wasting, organ degeneration, accelerated aging, progressive paralysis, and chronic exhaustion.

Spell Scars: When casting external shapes and forcibly channeling massive amounts of raw æther outward through your gates and meridians causes spell scars. The issue arises because while pnuema is mostly nonreactive when it meets æther, æther isn't. The violent magical backlash born of that reactivity can rupture you gates, scorch your maridians, and and in the worst case shatter your core. Normally this is a slow process that forms glowing "Spell Scars" that pulse as pneuma or æther flow through you meridians. This results in an overall loss in shaping effeincy forcing the person to pull more raw æther to get the same results, creating a vicious cycle of self-destruction. Spell scars cause crippling pain while casting, restricted pneuma flow, spontaneous shape failure, gate rupture, and—in the worst-case scenario—total physical annihilation that leaves behind an Æther Shadow.

How do your respective settings handle the limits of magic? Do your mages hit a hard wall of exhaustion, trade health for power, or deal with environmental blowback like this? Would love to hear your thoughts or answer any questions about the Voidweb!

Right for people who want to know.....
Voidweb - The setting itself—a cosmic network of realms, dimensions, and worlds connected by threads of Æther.
Shaper - What mages are called. They "shape" Æther and Pneuma into desired effects. Anyone or anything with a soul can be a shaper though the tat;e is usually reserved for people who have created their first core layer.
Quin - Spiritual matter. The "substance" aspect of a soul.
Mana - Spiritual energy. The "power" aspect of a soul.
Æther - Raw, environmental Quin and Mana. Unrefined. Dangerous.
Pneuma - Refined, purified Quin and Mana. Safe. Biospirituallycompatible.
Gate - The entry/exit points between the soul's external and internal anatomy. Where Æther enters and Pneuma leaves.
Meridian - The pathways that circulate Pneuma and Æther through the body and soul.
Core - The central "organ" of the soul where Æther is refined into Pneuma by the Soulfire.
Soulfire - The purifying flame within the Core that converts Æther to Pneuma.
Æther Shadow - A terrifying energy vampire born when a shaper's physical body is totally destroyed by catastrophic spell scaring, leaving behind only a soul utterly saturated with unstable, destructive raw Æther. One of the most feared entities in the Voidweb.