If you wield this and have 30 Strength, on a critical hit, the flail automatically casts the spell Atomic Fireball centered on the weapon.
Atomic Fireball.
10th-level evocation.
A bright flash explodes centered on a location with a radius of 500 feet and deals 100d8 fire damage, 100d8 radiant damage, and 100d8 thunder damage. Atomic Fireball deals 1d4 poison and 1d4 radiant damage each day to any creature that took initial damage for 30 days. Atomic Fireball also desecrates the ground, similar to the Hallow spell, causing any creature that enters to take 1d4 radiant damage each day and each creature must make a DC 18 Constitution saving throw when they take damage. On a fail the target is poisoned for 1 year and takes 1d4 poison damage each day. This desecration effect lasts 10 years and cannot be dispelled save for a Wish.