This rune effect causes a squadron of eight shadow beasts to plummet from the sky, dive-bombing on a targeted location and hitting for 60% weapon damage each. Impacted enemies will also receive 2 seconds of stun.
The basic skill emulates the "massive wave of arrows" type attack that's popular in medieval and martial arts films, with various demonic/magical modifications from the skill runes. You can see all six functions in the movie below. Turn it up to 1080HD, and play it full screen for the best visuals.
Note that this video was obtained via data mining with an emulator. It was not released by Blizzard and there will likely be some modifications to the runestone effects in the final game.