So the flash is known as the guy that runs pretty fast although he gets way less credit than he deserves. So firstly, how does he control himself when running so fast? Wouldn't everything be a blur? Well the speedforce(the thing that makes him fast) also allows him to process information at a much faster rate. He has been said to have a mind as good as a supercomputer. This is a huge understarement. So, time move slower for him so he can have more control but how slowly does he experience time in? "Less than an attosecond" A -blam!-ing attosecond. That's 0,000,000,000,000,000,001 seconds. It is literally impossible for a human to understand how short an attosecond is so let's give some comparisons. 12 attoseconds is the shortest period of time we can even measure. In a second, light can travel 7.5 times around the world, in an attosecond, light could barely move from one end of a molecule to the other. One attosecond compared to a second is like 1 atom compared to this entire planet, times 100. If you were immortal and living in that timeframe, you could experience everything from the birth of the universe to present day in less time than it takes for the average human to blink. To top it off, the flash said "[b]less[/b] than an attosecond" Ok so he basically has so fast reflexes that light itself seems to be frozen solid, what else? So we all know "E=MC^2" right? It basically says that the faster something moves, the more energy it will have. When moving at light speed every single one of the flash's punches have the power of a white dwarf star. That means that he can hit at somewhere between half to one and a half times the mass of our solar system. Each one of his punches is the equivalent to being smashes by multiple planets. Keep that in mind. Now what is the fastest the flash has ever run? Sp fast that it exceed multiple laws of physics and all logic of course. He was able to move faster than instant teleportation. He moved faster than planck time which is the shortest period of time theoretically possible. How fast was that exactly? 23,759,449,000,000,000,000,000,000,000,000,000,000,000,000 times the speed of light. Not only can he now move anywhere in the universe at any time but remember how he could punch with the power of a white dwarf star? That was at one times light speed. So now a punch from the flash now has the power of 23,759,449,000,000,000,000,000,000,000,000,000,000,000,000 white dwarf stars. This is easily enough to destroy the whole milky way and probably all of the known universe. Now that's just one punch. At that speed he could put out billions upon billions of punches per second. Also it would take a human 36 days to accelerate into just 10% light speed or else they'll die. Flash goes to 23,759,449,000,000,000,000,000,000,000,000,000,000,000,000 times light speed instantly. To be able to do that his body would have to be so strong that he wouldn't even notice notice if he got hit with the force of multiple supernovas. Doing to math on this would be near impossible but no known force in the universe would even be strong enough to slightly annoy him. Not like anything would hit him seeing as he could experience millions of years of time before light even moved from one side of a room to the other. He can move anywhere in the universe in an instant so good luck running away. If he needed to he could just punch with millions of times the force needed to destroy to milky way billions of times a second. He has no direct weakness and good luck suprising him seeing as he has billions of years to think and plan each second. Superman can punch pretty hard i guess.