Ghost of the Mere is an adventure for 12th-level characters, set during the time of the Tyranny of Dragons. It’s designed so it can be run as an additional quest during Rise of Tiamat. You’d benefit from owning Hoard of the Dragon Queen for information on Castle Naerytar.
The adventure sets up an interesting situation where the characters are sent to stop the black dragon of the Mire of Dead Men but must deal with a rising undead threat at the same time. The adventure’s structure isn’t linear. The interaction with the various characters in the adventure, including the lizardfolk Snapjaw, a captured Dragon Cultist, and three hags, allows the play to take several paths.
Most of the play surrounds three key locations: Castle Naerytar, the ruined Uthtower, and the Dragon’s Lair. There’s a focus on running the big dragon battle well, and the locations are interesting places to use.
The encounters can be very challenging for the players, with a lot of moving parts.
The main problem I had was trying to work out the shape of the adventure. The adventure assumes the characters begin by talking to the lizardfolk of Castle Naerytar; however, an introduction for the characters that explains their mission and sends them to the lizardfolk is missing in two of the three hooks. There’s also a lot of text. Lots of background details, occasionally in places that disrupt the flow of the adventure. It’s not easy to read.
It’s sort of a sandbox, as it doesn’t dictate how the adventurers must approach things. There’s no map of the swamp, but the key locations have maps.
There’s a lot of ambition in this adventure. It demands work from the DM to pull it together, but there’s enough here to make it intriguing.