All violence featured in the film is infrequent. Mostly all happens during the last act. It can be brutal with heavy injury detail at times.
Batman, Superman, and Wonder Woman battle Doomsday throughout Metropolis. Every time Doomsday becomes more powerful he emits an extremely destructive shockwave causing devastating chaos. There are several instances of Doomsday brutally beating Superman and throwing him into buildings. Wonder Woman cuts off his arm with a sword.
Lex Luther cuts his hand with a large knife. We see quite a but of blood dripping from his hand.
There is a brief gun battle in the deserts of Africa. People are shown being gunned down, and it is implied that their bodies are being burned to make it look like Superman had killed them. During the African desert scene a man is executed by being shot in the head offscreen. Superman violently slams a terrorist through at least five brick walls. This happens really fast and suddenly.
There is an extremely intense car chase between Batman and several mercenaries. There is a lot of gunfire and cars being destroyed with people inside of them. This scene is really dark because it shows Batman killing people.
Batman brutally beats and bashes several mercenaries inside a warehouse. Men get shot in the chest with his grappling gun, their bones broken, and they are shown being thrown into walls and through the floors in an extremely brutal fashion. Batman is also shot a few times and stabbed in the shoulder. A man carrying a flame thrower dies due to the flamethrower exploding. A man is also killed by a grenade.
In the Ultimate Edition, some of the fight scenes are extended (like the warehouse fight) and more brutal (like the knightmare scene)
The first half of the movie is very light on violence or action, apart from a city destruction scene and a car chase. In the second half, there is frequent violence involving gunfire, explosions, superpowers and hand to hand combat yet little to no blood is shown throughout the film. There are several implied deaths, but very few are shown.
The opening scene shows a child's parents being murdered in front of him. Although nothing is really shown, in terms of bullet impact, the scene may be too emotional/distressing for some. The father goes to punch the attacker, but is shot offscreen and then the mother wrestles with the attacker before being shot, again, offscreen. You see the parents' faces as they die.
A scene of mass destruction is shown as several dozen buildings collapse and explode, implying thousands or tens-of-thousands of deaths, but not a single one is shown onscreen. A man is found with his legs crushed beneath a large object, implying they are crushed, but aside from him not being able to feel them and some amount of blood there's not much more, in terms of injury detail, to that scene.
There are several screams and loud noises heard offscreen. A man is found with blood dripping from his mouth, and a bat-symbol, burnt onto his chest like he's been branded. Disturbing photos show a man who's been killed in prison as result of his "bat-branding". The burn mark is shown again, briefly. This scene may frightened some viewers.
In a dream/vision, a group of soldiers shoot another group of men with no blood. Then a vigilante fights the soldiers, punching and shooting them, before snapping a man's neck, which is shown and heard. Later on in the dream/vision, a superhero walks towards the restrained vigilante who's now tied up before he shoots lasers at the two men next to the vigilante, killing them offscreen. Their muffled screams and the splatter of their guts is heard. The superhero shoves his hand into the vigilante's chest implying he is going to rip his heart out.
At a senate hearing, a bomb in a man's wheelchair goes off, implying that everyone in the room, except the superhero, who appears to suffer no injury from the explosion, is killed.