Flash vs. Deathstroke with a Twist
The twist is that this is in real-world physics. Real-world physics say that an item cannot go faster than the speed of light because atom's structure would fundamentally change and get infinitely massive. Meaning, if Flash were to go faster than the speed of light, he would grow to be infinite in mass. So, Flash's speed limit is the speed of light. I'll allow everything else that makes Deathstroke who he is. So, who wins?