Rules: You can use LP instead of AE to cast spells. You must spend at least 1 AE per spell. Doing so is very painful and requires a successful Self-Control check. If the check fails, so does the spell (and like any failed spell, you must pay half the normal cost). You must pay for spells with AE first, and can only draw from LP when too few AE remain to pay for the spell.
Requirements: COU 12
AP Value: 10 adventure points
Publication: Core Rules page 284