Can Pluto conjunct the Ascendant make someone appear 'darker' than they really are?

You can completely control it and make it whatever works for you. I mean...the Bieber guy has the same placement. I call it charismatic. Your focus may be intimidating to others, but a loner in the worst sense of this word you can become only if you manipulate your powers and play. If you develop a concept of mutual power, become reasonable with issues of self control and control of others, you’ll be far from "dark", but kind of influential transformer.