From publisher blurb:
Tactical Doctrine: Rat King is a 5e-compatible supplement of ratfolk and sewers for players, GMs, and solo players.
Rat King comes with the Tactical Rogue class, a Rogue with a new skill trick for each skill you have expertise in. You can spend a skill trick to activate one of two powers or to gain advantage on a roll using that skill. If you have expertise in Acrobatics, you can use a bonus action to disengage and dash, or you can pass through enemy squares freely and attack an enemy with a bonus action as you pass through, or you can get advantage on an Acrobatics check, but once you use one of these abilities, the entire skill trick is exhausted and you can't use it again until you've finished a long rest. You'll have to make tactical decisions about which trick to use and when to use it. Like all the tactical classes, the Tactical Rogue still has the core features of the SRD Rogue, like Sneak Attack and Cunning Action, and has subclass levels at the same place as the core Rogue, which means any subclasses compatible with the core Rogue are also compatible with the Tactical Rogue.
As the GM, unleash the forces of the Rat King with the ratling skirmisher, heavy, shaman, swarm of rats, and wererat, who work together to form a deadly rat swarm. Expand your collection of mimics with new additions like the house mimic that eats anyone who steps inside or the potion bottle mimic that bites off the tongue of anyone who tries to take a drink.
Or play solo, taking on both the new monsters as well as some old sewer beasts like carrion crawlers, otyughs, and hook horrors with solo tables, randomly selecting from a variety of different tactics for each monster, which range from straightforward attacks to buffs and debuffs to deadly, cinematic finishing moves. Take your solo play to the surface with new solo mysteries, turning a sourcebook's city gazzeteer into locations where you can find clues, dodge ambushes from an enemy conspiracy, and get to the bottom of a plot to sacrifice humans to a dark god/subvert the city's government from within/steal everyone's left sock.