Watching the Witcher and similar fantasy shows, many casters can power their spells well beyond reason with their own life force. That might be a great thematic power to add to a cultist or dodgy Wizard.
Talent: Energy Sacrifice
Caster may opt to sacrifice their own health to power their spells. Before rolling a casting check, the caster decides how many wounds they will sacrifice to attempt to boost the outcome. If the caster succeeds their roll, the lost wounds add +1 SL each. The caster also gains one Fatigued Condition.