So um... spoilers ahead.

The video game Injustice: Gods Among Us did a very surprising thing and had D. Grayson killed off. Instead, the primary Nightwing of that game's story mode was Damian Wayne.

As revealed in the prequel comic based on this game, this was not to be the end of Mr. Grayson's story in this universe. After Boston Brand (Deadman) was wounded to the point where he was going to fade away, by the mysterious new Specter, Brand chose Grayson to become his successor. Thus, Grayson is the second Deadman.

Deadman II is just a simple repaint of the standard Injustice Nightwing.