It’s no secret that Superman has a wide array of superpowers, including super-strength, flight, x-ray vision, super-hearing, and more. Having so many abilities is partially what makes the Man of Steel one of the most powerful superheroes, but it's the most modern addition to his superpower catalogue -- an attack called the “super-flare” -- that also makes him one of the most dangerous.
The addition was first made in Superman #38, published in 2015, with Superman engaged in a fight with Ulysses (a character introduced in Geoff Johns' Superman run). Ulysses, whose real name is Neil Quinn, was originally from Earth, but was sent to another dimension by his scientist parents, who feared their planet would soon be destroyed. Sound familiar?
Much like Superman, Ulysses gained extraordinary abilities from his new world's environment, including super-strength, super-speed, flight, and energy transference. After returning to Earth and realizing he was not the last of his kind, Ulysses reunites with his parents, and all seems well. He even offers to bring six million people from Earth to his new home, called “the Great World,” for a fresh start. However, Ulysses's gesture of kindness turns out to be a ruse, as he really plans on using those six million people as fuel to power the Great World's core. Ulysses subdues Superman, but after learning his parents snuck aboard the ships bound for the Great World, he has a change of heart. He frees Superman and the two of them save the people, but as a result, the core becomes unstable and explodes, destroying the planet.
Back on Earth, Ulysses blames Superman for his world’s destruction, and a fight ensues. Imbued with immense energy from the Great World’s destruction, Ulysses threatens to unleash that power to destroy Earth. To stop him, Superman tries to use his heat vision, but it quickly grows out of his control. The beams become more and more powerful until a massive blast of energy erupts out of Superman’s entire body, incapacitating Ulysses and incinerating just about everything in sight - including most of Superman’s clothes.
After passing out from the effort, Superman wakes up in the Bat-Cave, where Batman- who showed up in the knick of time to bring Clark to safety- explains what happened. Superman’s heat vision works by essentially releasing the solar energy that gives him his powers as concentrated beams through his eyes. However, Batman tells Superman that his heat vision is merely “a precursor to another ability…You unleashed the energy stored in every one of your cells. You created a solar flare, Clark. A super flare.” Batman admits that he’s almost jealous that Superman gained yet another superpower on top of all the ones he already has, and that he would be concerned about that level of power in anyone else. However, much as the heat vision slowly depletes Clark’s solar energy, the super-flare uses it all up at once, leaving Superman essentially powerless for the next 24 hours until his cells recharge.
Batman may trust Superman with his new power, but Superman has a hard time trusting himself. He could barely control the super-flare when it was happening, and the blast destroyed everything within a quarter of a mile. Things were stressful enough for Superman when he just had to worry about breaking stuff - now, he’s essentially a walking nuclear bomb. Still, if he could get it under control, the super-flare would definitely come in handy.