My muse? Well, lemme tell you a lil story, Anon. (Y'could just go to his 'about' page on my blog, but I'll just sum it up real quick.)
Shadowplier, better known as Shadow, is the guardian of the lovely Markiplier. He took the form of Shadowplier the moment Mark drew his first breath in the world. He looks like him, aside from the vast colour difference. Shadow's got monochrome skin that changes tones in the light, white eyes, white blood, and two different forms. His hands don't have fingernails, but instead end in sharp claws. He's intelligent, caring, mischievous, and sometimes silly.
Considering that he's Mark's shadow, the two share a lot of similarities. Shadow's as old as time itself, and has had many past lives. Each regeneration causes great pain to his body that can last up to a week. It's...bad. In a few of his past lives, he's been the shadow of very bad people. Although he can't remember a lot of his previous lives, he can remember being rather...murderous. He is still prone to these homicidal thoughts, though he'd never harm a hair on Mark's head. He loves him dearly, and would do anything for him. I mean, it is his job, after all. Shadow's got different AUs, and in two of them he's got a lover. Their names are Ceno and Aludra. (If you want to know about them, I highly suggest clicking on his 'about' page, as it provides links to their blogs.)
Shadow's pure shadow form is definitely different. It's in this form that he is the most deadly, and he knows it. He's got many methods of killing, one being to snake tendrils of shadow into the victim's eye sockets and override their brain, causing them to seize up and, well, die. He tries not to give into his darker thoughts, but there are times when he can't do anything about it. In that event, he asks his Master if he can leave, does his business, and comes back to self loathe. When The Creator formed Shadow, he knew that there was something different about him. After a few hundred years of his life, The Creator noticed that Shadow was a rogue. Shadow would often drift between the realms when he should have been doing his duty. Shadow-beings are an elusive species that are very hard to track down. Shadow, however, didn't care enough to keep himself hidden. He'd always make his presence known in some way, and when he had been assigned to Mark, it was no different.
The real difference is that before, with past assignments, he could leave the patron any time he pleased with no side effects. Or, no side effects other than the past Master being pissed at him for leaving if that were the type of person they were. Now though, if Shadow leaves Mark without permission or for too long, he succumbs to massive seizures that could land him in a medical ward.Shadow's a compassionate being, and he doesn't like to give up on people he cares about. He gets along with most anyone, but won't back down from a fight if it calls for it. In short; he's pretty rad.(Sorry that that was so damn long. I was trying to cover most the bases.)