They haven't shown us how he's back from the dead when he died in front of tea and had a funeral.
Since OLTL has been back they showed him escape from a bulding wearing a black hooded sweatshirt, kill some guy who was after him, and that he now has a tattoo of some symbol on him.
He then lurked in the shadows and stalked todd, following him into Blaire's new night club where everyone was saying "s-h-i-t" a lot and Dannie overdosed on drugs.
he then revealed himself alive at the hospital where dannie is while todd was calling Tea a "s-h-i-t-t-y" parent, where blair, jack, vickie, todd, etc. didn't act surprised at all to see him alive