Shadow Evocation, Greater (Caustic Eruption)

You tap energy from the Plane of Shadow to cast a quasi-real, illusory version of a caustic eruption spell. Acid erupts from your space in all directions, causing 1d6 points of damage per caster level (maximum 20d6) to creatures in the area. If an affected creature succeeds at a Will save to disbelieve, it takes only 60% damage from the attack. Each of the next 2 rounds, creatures that failed their saves against the initial burst take an additional 1d6 points of acid damage per 2 caster levels (maximum 10d6) unless the acid is dispelled. Each round, this creature can make a Will save to disbelieve and take only 60% damage.