saveourearth sounds like a pretty perfect fit with your preferences. It's on DW, slow but steady-going, very backtag friendly and has a ten comments AC (with the time when the thread was started being irrelevant, only the tags need to be from the current month). It's mem-loss/AU (both, actually, because characters get reincarnated into an AU and regain parts of their former self, but the AU is real) and powers and memories can be regained. Technically you don't even need to humanise because you could reincarnate a character as an animal, too. There's plot, too. No castmates though, sadly, and while there is the odd horror element, it's not a horror game. I'd say it leans more into the adventure genre, despite the setting being a town? But it's a bit hard to describe for me. The game ad is here, if you wanna check that out.