This Twilight Forest boss has a 3 phase fight. In the first phase, he wields a scepter and shoots a combination of Ender Pearls and Ghast fireballs. He has two decoy ghosts that are immune to damage and shoot Ender Pearls and fireballs similiar to a ghast's. You have to hit the Ender Pearls back at the non-illusory Lich or use splash potions of healing in order to destroy his 4 shields, otherwise he is completely invincible. In the second phase, he will use 1 of 3 scepter abilities. Deal accordingly. In the second phase of the fight, he is wielding a Golden Sword. Just kill him quickly. During phase 3, the Lich will spawn various armor-clad zombies to fight you. These zombies are of a greener and more durable variety. You can fight them off individually, but killing the Lich will destroy his minions.