The leader of the Prolethean cult in Season 2 is Ari Tasarov.
I Knew It: Helena's survival was predicted by a large enough portion of the fanbase that there was a Fan Nickname for it: "The Ballpit of Denial". Ok, fair enough. What pushes this into truly eerie territory is the explanation for her survival: she is a mirror twin, and her heart was on the reverse side of her body as everyone else's. This exact explanation was predicted by fans from the mere fact that she is left-handed.
Ari Millen qualifies as well. During a red-carpet appearance just a week or two before the Season 2 finale and the reveal that Mark was a Project Castor clone, an interviewer asked him if he'd be interested in playing a clone character. A deadpan Millen claimed it would be too much work for him. Kevin Hanchard (who was standing next to Millen) cracked up on camera; the interviewer never caught on. See it here.
Plays Great Ethnics: Tatiana "Tania" Maslany, is Romanian-Canadian. A sort of female counterpart to Tony Shalhoub.
Promoted Fanboy: Patrick Adams (of Suits fame) has stated that he loves Orphan Black and of Helena in particular. He has a guest spot in "To Hound Nature in Her Wanderings" in which he gets to romance Helena very, very briefly.
Real-Life Relative: Alison's adopted children, Oscar and Gemma, are played by siblings Drew and Millie Davis.