From Archon Arcana - The KeyForge Wiki

Anomalies are cards that are released as part of an expansion set, designed for a future set. Rather than appearing consistently as part of a house, they will show up in any of the 7 houses of the set where they are an anomaly. Sometimes they may be very powerful, with few counters in the current set. Other times, they may be really boring, because the mechanics needed to make them work aren't in the set.