A nicely gothicky spooky type of Gamma would be good.
Actually, I think we haven't had a seriously spooky gamma in a while. Partly because better understanding the Anomaly makes it less unsettling for the team, and hence for us. But, you know. Regular serial killers are limited in what they can do to people only by physical laws. Gammas ... aren't. Necessarily.
By spooky I don't mean just horrible. Felicity Tabor was horrible. Simon Talliwell was spooky.