Circle of Ruin

You slam your staff to the ground to summon a 20ft magic circle that increases all party members' chance of inflicting critical spell strikes.

While you or your chosen allies stand in the magic circle the number you need to roll critical spell strikes is reduced by 2.

At Higher Levels:  When you cast this spell using a spell slot of 6th level or higher, the number you need to score a critical hit is reduced by 1 for each slot level above 5th.