I managed to get Moon Lord down to 44k health after almost dying to Vortex Pillar and having Moon Lord spawn when I was at 340/500 health.
By the way, my current accessories are Spiked Destroyer Emblem, Violent Feral Claws, Spiked Warrior Emblem, Warding Power Glove, and Angry Avenger Emblem. I am using a full set of Beetle Armor, with Scale Mail, and a Murderous Terra Blade as my main weapon. Also, I’m using the UFO mount given by the Cosmic Car Key.