To me, Dark is still a master manipulator, so He’d obviously have a good handle on different manipulation tactics… including playing the sympathy card. And Who Killed Markiplier? being split into chapters, that seems very much the Host’s style. He was the Author of many books, after all.
The portrayal of Dark made me very emotional and sympathetic for our Big Bad… but then, when I examined my feelings, I realized that our highly-charged reactions was probably what the old schemer wanted in the first place. He wants us to let Him in, and what better way to have our hearts and minds open to His control than for Him to appear as if He was not originally a villain after all, but in fact a Fallen Hero? A well-meaning man who became consumed by vengeance?
It’s a story that makes Him relatable, yes, but it also weakens our resolve to stand against Him and it paints Mark as the bad guy. It turns everything we know topsy-turvy. And that’s exactly what Dark would be looking for.