New TN = 9 + (MP / 2 [rounded down])
The value you rolled for the Fatigue test becomes the TN that the targets or those affected by the spell will use for the resistance test. Any spell in which the caster would have made an attack roll vs the targets Defense changes to a resistance test vs the targets Dexterity (Acrobatics).
First, you can simply fail by not meeting the Fatigue TN. When this happens, you move down the fatigue track towards dying (explained later).
If your failure included doubles on any two of the dice, your attempt becomes a miscast. The severity of the miscast depends on the Stunt Die. The Stunt Die face of 1-3 is a minor miscast and a Stunt Die face of 4-6 is a major miscast. Then simply roll on the appropriate Miscast table below.
D6: Minor Miscast Table
1. You keep the magical surge under control.
2. A brilliant show of magical energy escapes, but no adverse effects.
3. A local random minor effect occurs
4. A local random major effect occurs.
5. The spell you failed is forgotten until the end of the encounter.
6. Your spell casting stops working until the end of the encounter.
D6: Major Miscast Table
1. A local random major effect occurs.
2. The spell you failed is forgotten until the end of the encounter.
3. The spell you failed is forgotten until a your next rest.
4. The spell you failed is forgotten for D6 days
5. Your spell casting stops working for D6 days
6. Test Constitution (Stamina) vs Casting TN to avoid immediate death. Succeeding the test still means you fall unconscious, but alive, and your spell casting stops working for D6 days. Fail and you die explosively.
Fatigue Track
To limit the potency of magic, there is a Fatigue Track similar to the Injury Track. The conditions are:
Winded: -1 to all tests
Fatigued: -2 to all tests
Exhausted: -3 to all tests
Dying: Dying