Ongoing theories: There is not a defined opinion about this attribute on the internet. The devs didn't came out with an official explanation about this stat, and even today people still debate this on chat. The following are explanations to the stat, based on internet communities:
From Trove forums: It's a joke
I'm 100% sure superstition increases your superstition.
From Trove Forums - part 2: It's a joke
It definitely might do something.
And of course there is some crazy conjectures like "the ability to drop more pembocks".
From Trove Wikia, they think it increases magic defense.
Found on the Qubesly and Samantha pet (Allies) . Possibly increases magic resistance.
And on reddit, it's still a ongoing question. Here and here.
Real answer: I know that answers need to be atemporal at StackExchange, but as an update to this, it seems that the real effect was found: Allows you to see the ghosts of dead players during the Shadow's Eve event. Has no effect otherwise. Some players at the forums believe that is a troll stat, some kind of garbage stat that never got removed from the game.