Nightmare Omni

In the story of SpikerMan, Omni is considered to be the most powerful bad guy in the universe and even though he technically dies in one major event, Omni's presence still lives on in the memories of the heroes.

Omni has rules that are connected to his life. He states that he cannot be killed by weapons, or the unnatural. Only the fists of his opponent can kill him. The heroes find this out when it seems one of the heroes kill Omni with a sword. His body stays dead for hours, and he comes back to life in pieces in a nightmarish form. He resurrects his physical body by willing it, and can no longer be killed the previous way that he died before. 

Sara goes through a traumatic experience where, years after Omni's death, it seems his spirit haunts her, and being haunted by Omni almost breaks her mind. She figures out eventually that her mind powers are creating a delusion of his memory, and she has to learn to suppress her fear of him as she regains her confidence that he is truly dead and can no longer hurt her.

Lord Gold Skull has the ability to manifest a person's greatest fear, and for Kelvar's case, it was Lord Omni. Kelvar had to defeat a nightmarish version of Omni, and he succeeded without Raven's help, as Raven was millions of light years away.

There is uncertainty involved in Omni's death, as they've seen Omni resurrect himself before. His dead body was sent into a large sun to burn away all traces of him. The idea of not knowing is one of their greatest fears.