City of Mist is a modern Mystery Pulp tabletop RPG made special by its two major concepts.
Rifts. You play as a Rift, a person with some an awakening story (Mythos) within them that seeks to perpetuate itself through you. The story gives you access to supernatural powers like the ability to manifest the elements or turn invisible. Why you are given access to these powers are the first mystery, leading into the second.
The Mist. The Mist is a force within the City that prevents non-Rifts from accepting, discovering or remembering Rift activity. In most cases the Mist simply distracts non-Rifts by attract their attention elsewhere, and in cases where this cannot be done memories can be erased. The events still happen but things like fire powers destroying a building would be credited to terrorists or a gas-line explosion. The Mist’s power seems almost limitless within the City and knowing of its existence often makes Rifts suspicious and questioning.
Mechanics.City of Mist uses a system familiar to other Powered by the Apocalypse games, but differentiates itself through the use of “Tags” familiar to those who have played FATE or Lady Blackbird. When asked to roll a “Move” you add together you beneficial tags and subtract your weakness tags, and then add that to a 2d6 roll. 7+ means partial success and 10+ a complete success. 6 and below triggers a move from the Master of Ceremonies (Game Master) which follow the same rules.
It is a very simple system, only slightly more complex than your typical PbtA game. But that small complexity really allows you to make a character your own. It focuses on Narrative and uses mechanics at important decision points to direct further flow of the narrative.
"Tags" refer to a series of Keywords. If a Tag sounds like it would be appropriate to a situation, then you add or subtract 1 to your bonus (based on if its helpful or harmful to the task). If I had the tag "Ninja" while attempting to swordfight on the top of a moving train, I could ask the MC if it applies. If it does I'd +1 to my bonus, along with any other tags that might apply.
Moves. Basic Moves in PbtA are incredibly suggestive of the feel the game is attempting to emulate. In the case of City of Mist it leans heavily into solving mysteries via exciting action. Much like the comic book art style of the rules book, the rules really play into pulp-styled adventures.
While the mixture of PbtA and FATE allows for interesting gameplay, there are a handful of other mechanics that make City of Mist more than a mash-up.
Crew Themes. Most TTRPGs are based on teamwork. City of Mist makes that all the more clear by making that part of the game. As a team, the players have a set of shared Tags that makes them, as a unit, more effective at particular adventures and encourages cohesion in concept.
Balancing Act. Maintaining a balance between your Mythos and your everyday life is a major theme of the game. If you become too much like your Mythos, you are overtaken by the story and do as it demands. If you neglect your Mythos and attempt to remain mundane you become a Sleeper like the rest of the City.
The Mist. As a narrative device I love the Mist. It allows adventures to be as wild and exciting as you want and then shift right back into the everyday life stuff that makes RPGs set in modern settings so compelling.