As much as I want hallucination!Oswald to have enough power over Ed to be able to touch him, please consider: hallucination!Os phasing right through Ed.
They’re standing so close together, close enough to touch, Ed’s looking into the watery whites of his best friend’s dead eyes. He thinks he can feel cold breath hitting his face. He watches as Oswald’s hand reaches up towards his shoulder, and it seems so real that he braces for the impact-
Only for the hand to rip right through him, a chilling numbness following in its wake, settling, freezing, into his bones. It’s excruciating; it feels like part of him is being forcibly torn out, leaving him hollow and empty and terrified.
He finds himself falling to the floor, hallucination standing over him, and he wonders if this is what Oswald felt when he hit the water.