4 Ways
bang
Man-Bat doesn't know who pulled the trigger, never will-someone new from Gotham PD, a gang member, a paranoid citizen with connections? Not knowing doesn't stop the blood streaming up from his falling body like a parody of puppet strings. He's not aware of anything when his massive body shatters the car he lands on.
whimper
The Batman tries, he knows, but the formula has twisted his body so much that there's nothing eather of them can do. The black glove wipes the blood from his weeping eyes and nose and mouth, but the only things that escape are half-sobs and choking wheezes, and he's blacked out before he can make any meaningful last words.
fire
His skin his skin his skin is burning and his eyes are melting in his head and oh god why couldn't Rumor have picked something else a gun a knife anything anything else-
frost
Langstrom is deep in the closed-off catacombs beneath Gotham. He doesn't have his formula, doesn't have echolocation, can't see his own pale hand in front of his face, and he doesn't have food or water. He still thinks Batman will find him, even as he pitches over into the cold, hard dirt and shivers and feels that he's floating away.