There's the Robber Bridegroom of course, and in the Old Woman in the Woods, they set the stage and then vanish like any good plot device. . . .
And then there's the variants of Snow White where she's found by bandits, not dwarfs. I think some people will allude to this one because they want their prince married off and figure that if he wakes a woman from enchanted sleep they figure they've got him caught, despite his father's order to not marry. . .
The thing is that that robbers feature in many tales as plot devices, not in particular types. I don't think I'm going to use the substitute letter one where the robbers decide to play a practical joke on a king by having his letter to have the bearer executed change to one saying he should be married to the princess at once.
Hmm -- though he could allude to it. All the more in that he thinks it's new orders -- or could at least pretend to believe it.