Marble Hornets didn't have too many ARG elements, just codes in the videos and a twitter account. The only Slenderman series I've seen actually be an ARG was EverymanHYBRID, where people were encouraged to go out and campaign for HABIT to take over, and there were real world rewards for completing tasks. The Seven Trials of HABIT was a real world game with implications in the fictional world, MH (and for that matter CL44) didn't have that. Eckvanet kind of has an extra layer of interactivity but it's just Troy and it's been slow moving as shit. I've never heard of a HTB ARG. a quick search just netted me people talking about his face reveal. I'm a purist when it comes to the definitions here, if there isn't a real world element, it's not an ARG. The Dark Knight ARG had real world shit, Year Zero had real world shit, I Love Bees had real world shit, even the Cloverfield ARGs had real world shit - if it's just codes and spooky videos it's not an ARG, it's a convoluted webseries.