This enemy is found only in the mobile and console version(s) of Terraria.
The Shadow Hammer is a stronger version of the Cursed Hammer, found in the Underground Corruption after the Wall of Flesh is defeated. Like all shadow or spectral-class monsters, it is exclusive to the Console and Mobile versions of Terraria.
Its attack pattern is the same as its weaker variant, that is by spinning and then charging at the player. Once hit, it will restart the spinning motion.
The hardmode bars that the Shadow Hammer drops are world-specific, meaning that they will drop the bars according to which ores the world has been blessed with (e.g. In a world blessed with Palladium, Mythril, and Adamantite, it will drop one of the three bars at random).