The Casey is a post-Moon Lord charged melee weapon bought from the Scavenger in True Mode.
When the left mouse button is held down the bat will be held out and will start slowly being raised by the player.
Once fully charged the button can be released to reflect enemy projectiles and deal massive damage to enemies within melee range.
Only projectiles that deal less than 1/8th of the player's maximum health can be reflected, as well as having to be smaller than 32x32 pixels.
Each of the reflected projectiles can hit an enemy individually, with its own independent cooldown.