It has low damage, slow attack speed and short range but still can auto every bosses include calamity or thorium.
「Umbra」almost broke the game, the Timeless Potential can resurrecting you not only once, instead , if the buff exist you could never die
Hope to see this bug fix soon since it’s really broken, I playing with my friend and he auto Polterghast after defeat MoonLord with this 
Terraria Mods Wiki
Umbra is a Spatial weapon that can be obtained after the Lunatic Cultist has been defeated, attacks with this weapon will sweep in an arc and unleash fast, will piercing Timeless Blades