This is the SuperDraco thruster. According to SpaceX, eight of these engines will allow the Dragon V2 spaceship to land anywhere in the planet with the same accuracy of an helicopter. Here you can see it in action, during the last test of its final certification.
https://gizmodo.com/first-look-at-dragon-v2-the-first-manned-spaceship-by-1583376826
During its presentation, Elon Musk said that the Dragon V2 capsule is going to be able to soft-land even if three of its retrorockets failed. And, if more than three fail, the new ship will have a set of parachutes for emergencies.
