Astute observations, Keeper of Knowledge. Allow me to elaborate on the finer details. When the first worthy terrarian bested the Wall of Flesh, the lizhards discovered a critical flaw in the Golem, only made clear by observing the terrarian's journey. The Lizhards worked tirelessly to repair the construct, but by the time the three mechanical bosses were deconstructed, golem was not fully operational. However, it was still able to put up a fight, but sending it out risked permanent damage at the hands of the terrarian. The Lunatic Cultist, at the time merely a powerful mage in the Solar Order, decided to take this matter into his own hands. Rallying some followers, they stole one of the ancient tablets that was being used as a failsafe for the Moon Lord Seal and used its power to eradicate the terrarian, destroying it and them in the process, so completely that neither could return. As a result of his impulsive actions leading to the loss of the tablet, the lunatic cultist was banished from the Temple. Bitterly, he and his followers left for the abandoned Derpling Laboratory, intending to use the advanced technology left there to create a weapon to destroy the Moon Lord. They were unsuccessful in this task, but they managed to create another tablet using the advanced derpling technology hidden in the dungeon along with the remains of the tablet used to incinerate the first worthy terrarian. However, before he could use it for anything, he recieved news of the Golem's destruction. Realizing that the seal was almost undone, he resolved to temporarily set aside his resentment and create a new layer to the seal, in a last-ditch effort to affirm that the terrarian was strong enough to destroy the Moonlord once and for all. This history may contain some inaccuracies due to being passed on for so long via word of mouth, but it should mostly be accurate. The specifics of Golem's critical flaw have been lost to time, but I believe it was something to do with the chains connecting the fists to the body, or perhaps the fists themselves.