Everyone knows a black cat is bad luck. Especially when you're in the middle of wrestling giant robots or twisted cultists.
For a while now, the black cat has been a regular feature of out Pulp Alley games. The cat starts at the centre of the table and moves d6" in a random direction at the start of each turn. If the cat collides with any character, they're in trouble. Once per turn, an opponent may force them to reroll one die. The bad luck lasts until the character expires, or the cat runs into some other unfortunate!
The rule works well. It's not a game breaker, but everyone tends to give the cat a wide berth.