Nightmare Fuel: Honestly, given that this story ups the already considerable darkness of Bioshock, it should be a no brainer that it has lots of nightmare fuel. Outside of elements from the game being expanded on, the greatest example of this is who most of the Total Drama characters have been shown to be slowly giving into the madness of Rapture in different ways.
Ship Tease: Gwen and Cody, and to a much lesser extent, Courtney and Noah.
Also, Courtney and Gwen, at least on Courtney's side. In the most recent chapters, Noah's joke about Courtney having a crush on Gwen might not be a joke after all.