Punisher :
Flash grenade against Dr. Light (would that work?) - then punishes him for raping Sue Dibny in a VERY nasty way!
Scarecrow - Dr Crane could use gas that gives him a phobia of guns/loud noises/blood.
Deathstroke :
Ringmaster - would the hypno hat work on a guy with one eye?
Who else? Feel free to suggest Hitman, Vigilante, Solo , Foolkiller etc.