The Crypt of the Bloodbat

Publisher's blurb: A short adventure for characters of 3rd level, with customization options for higher or lower level PCs. In addition to an interactive DM's map, there's a player's map of the Crypt and five new monsters, including the eponymous Bloodbats. There's also rules for teams — two monsters working together — and the Mourning Staff, a magic item that's usable immediately but grows more powerful when you attune to it!