How to Replicate: Using Grapple to drag allies to yourself puts stacks of Cripple on them. If you e.g. on a practice-server refreshes grapple and do it quickly again, it even stacks the cripple.
It's easily tested on allies in a practice game, but it's also viewable in a test-match i made with some buddies around 9min mark on ingame clock: 1982215