Shadow Zachary was born from the darkness in the real Zachary's heart. Thus Jolly Roger used that darkness to create a pure evil entity named (Shadow) Zachary.
For being born from the darkness of Zachary's heart, Shadow Zachary's personality is completely opposite to the real Zachary's personality. Thus he is nothing more than cruel, selfish, and most of all, pure evil. He seeks to only destroy and absorb the real Zachary so he can become truly powerful.
Shadow Zachary was nothing more than just Zachary's shadow. But after prolonged exposure to the powers of the Darkfire Cutlass, Jolly Roger used that as an advantage to create an evil, dark opposite of the real Zachary. Shadow Zachary carries all of the memories of the real Zachary, thus he knows everything he needs to know in order to destroy the real one. He first came into contact with LaMario, explaining to him who he is, and what he is plotting. He seeks only to destroy the real Zachary, Jolly Roger, and anyone else who stands in his way to world domination. But he must first destroy and absorb the real Zachary to truly live, and become more powerful. And he is willing to join anyone like the Co. Empire that will help him find the real him. And in return, he would give out the information, location, and Guild members of the Ocean Gods guild. Once Shadow Zachary was part of Shadow Illusion. But seeing the guild useless, he left in order to search for a better guild like the Co. Empire or anybody who can help him find the real Zachary. He plans on betraying Jolly Roger so he can control the Undead Army and begin his conquest for world domination.