It is relatively easy to beat the moon lord, well, if you the right gear. I used two deadly sphere minions, solar eruption, and vortex beater (And greater healing potions, of course.) What I did is: first, use the vortex beater to destroy his "hand-eyes." Next, hide below a 1-5 block thick layer of solid blocks, and wait for his forehead eye to open. Because the beam from his eye cannot pass through blocks, use the solar eruption to damage his eye through the layer of blocks. Once his core is exposed, just move back and forth to avoid the true eyes of Cthulhu. You may have to use the power of auto pause and nurse here. Remember to use potions as soon as you lose one fourth or less of your health. The armor I used was beetle armor, with worm scarf, celestial shell, band of regeneration, ufo mount, specre boots (For extra speed and extra flight time,) and steampunk wings.