Raph's favourite enemies were the foot soldiers from the alternate dimension.
He'd been convinced that he'd hate everything about that world. But when he'd accidently cut the arm off a foot soldier, he had seen robotics instead of blood.
At first he didn't know what to do, but he quickly realised what it meant to him; It meant that he didn't have to hold back.
He stopped thinking about his actions; ignoring all the lessons he'd been given on reining his anger and power.
It took longer for him to regain control, but it was worth it while it lasted.