The best supplement for Mage: the Awakening that I've read so far. A lot of good ideas for investigative horror scenarios. The intruders/antagonists/challenges are creative, scary and presented in a way that make them feel easy to incorporate in one's own campaign. Every intruder has suggestions of how it is manifested, how it behaves, how it evolves and how it can be banished (seldom by violence). The book also contains a meaty section with general information about the Abyss.
[5 of 5 Stars!]