When the story "arc" for Tempest and the rest of the block was being fleshed out, the writers thought it would be cool if each of the major races on Rath--the Kor, the Vec, and the Dal--had a jinxed item that was part of some greater whole.
The original intent was to put Jinxed Idol in Tempest, Jinxed Ring in Stronghold, and Jinxed Brooch in Exodus. The Brooch would spell out what happened if all three were in play simultaneously. Unfortunately, the whole idea was scrapped before Exodus was designed, so it was never really determined what Jinxed Brooch would do by itself, or what would happen when all three were combined… although it was probably something catastrophic.
The art for Jinxed Brooch had been commissioned in advance, however, and ended up on the Exodus card Null Brooch.