This addon introduces the Black Silence, a character from Library of Ruina as a difficult, almost unkillable boss.
He does not spawn naturally, only in creative menu. He is a master of evasion and endurance fighting. With only 999 HP, he can dodge, block, and counter attacks. He possesses a "stagger-meter" which has 500 HP. Once it is killed, the Black Silence can be hurt.
In combat, the assassin has 9 weapons to switch to, including a ranged weapon. Each of these 3D weapons possess different abilities. The weapons deal 100 damage each along with their special functions.
An example, the Old Boys hammer. It will launch enemies up in the air. The rest you will have to see for yourself.
He bears no drops, once killed, his disappears as if he never even existed.
I may make an easy version you may be able to beat in survival..