This is something I was lucky enough to find when it had just started, and I felt like you guys would definitely enjoy it in the downtime of the Soulstorm ARG. Although one thing I will note is that this ARG is less interactive (similar to the Oddworld Soulstorm and Overwatch Sombra ARGs) and more immersive (similar to the likes of Marble Hornets).
Petscop is an ARG about an unfinished, unreleased Playstation 1 game developed in 1997 by a company called Garalina. The story so far has progressed through a series of uploads over on the
Petscop YouTube channel that take the form of gameplay uploads. As of this post there are currently nine uploads.
The horror is less jumpscarey and much more subtle as the player Paul progresses through the game, which seems to mirror real world events and cases of child abuse. In my experience of ARGs Petscop is a unique take on how an ARG can be constructed and definitely pays off if you're able to immerse yourself in the narrative being laid out for you. If you have a taste for creepypasta, ARGs, or just want something to occupy yourself with for an hour or two, then I'd highly recommend watching this ongoing ARG.