You obtain another two primary domains: Darkness, and Evils, alongside two new secondary domains in Pain and Chaos, your power significantly grows, and can grow further through the sacrifice and suffering, of others, and yourself.
Upon Walpurgis Night your power grows severalfold, the creatures of evil gather below you, an infernal army from the abodes of darkness, and slaughter all who dare oppose you, only ending their rampage when dawn rises overhead.