You blend shadow into your spells, increasing their efficacy at the price of susceptibility to light.
BENEFIT
When you cast a tenebrous spell in darkness or dim light, the spell’s effective caster level and any associated save DCs are increased by 1. Any attempts at dispelling a tenebrous spell in darkness or dim light take a –2 penalty on the dispel check. Casting a tenebrous spell in bright light is difficult, and requires a concentration check (DC 15 + twice the tenebrous spell’s effective spell level). Attempts to dispel a tenebrous spell in bright light gain a +4 bonus on the dispel check.
MP Increase: +1 (a tenebrous spell costs 1 additional MP more than the actual MP cost of the spell.)