Fight Killer Croc, Deathstroke, Copperhead and TN-1 Bane as Deathstroke.

Put the folder "Deathstroke_Boss_Fights" to your "%installation directory%Batman Arkham OriginsSinglePlayerDLC%anyfolder%" folder.

After the game checks for DLC, make a new save file and press:
F1 - to fight Killer Croc
F2 - to fight Deathstroke
F3 - to fight Copperhead
F4 - to fight TN1-Bane
F5 - to fight Killer Croc(Injustice Suit)
F6 - to fight Deathstroke(Injustice Suit)
F7 - to fight Copperhead(Injustice Suit)
F8 - to fight TN1-Bane(Injustice Suit)
F9 - to fight Killer Croc(Judas Suit)
F11 - to fight Deathstroke(Judas Suit)
F12 - to fight Copperhead(Judas Suit)
P - to fight TN1-Bane(Judas Suit)