Knight Terrors: First Blood kills off a long-standing DC character

gamesradar.com:

Knight Terrors: First Blood - the opening issue of DC's horror-themed summer event - is here, and it kicks the saga off in suitably dramatic fashion. If you're at all worried about spoilers for the issue, then now is the time to look away, as we're going to get into what happens in First Blood - and who is seemingly killed off - in detail.

The new issue, written by Joshua Williamson and drawn by Howard Porter, opens on John Dee - AKA DR Destiny - enjoying a pleasant dream about his family. That's soon interrupted by a sinister presence. Dee tries to fight back, but the dark entity overpowers him.

Cut to Boston Brand - Deadman - the narrator of the issue. Tracking Superman, Wonder Woman and Batman, he learns that something is haunting the world's heroes. Following them leads everyone to a locked room within the Hall of Justice, which Batman opens, only to discover the corpse of John Dee.

This, we soon discover, is actually a bit of a ruse. A call from Harley Quinn reveals that Dee is still in Arkham Tower - comatose, but alive. The heroes rush to the scene, only to witness something tear out of Dee's body, leaving him deadso for real this time.

The rest of the issue sees this new nemesis, named Insomnia on the final page, start to enact his grand plan. A slew of characters as diverse as Superman, Nightwing, the Joker, Hal Jordan, Ravager, and the Flash are all seen succumbing to nightmarish delusions.

But what exactly is his scheme? At one point, Insomnia cryptically says to Batman that he wants the world to "finally see superheroes the way that I see them. Not as heroes. But as horror." He also, on the final page, says that he wants to make them "pay for what they did to me." 

That's clearly setting up a mystery over