The DC live-action film Green Lantern was released in 2011 with disastrous results. Even after a decade of non-stop superhero film releases, it still lives on as one of the worst live-action superhero movies of all time. Warner Bros. and DC (and nearly every movie watcher in existence) decided to ignore Green Lantern and move on to other projects. However, in everyone's haste to move past it, people missed one of the largest displays of power ever shown in a live-action superhero film. In hindsight, the oversight makes sense, considering the monumental power move doesn't take place in the final battle but during an awkward training sequence.
After Hal Jordan (Ryan Reynolds) receives a Green Lantern power ring from a dying alien, he is transported to the planet Oa. There, he receives training from the bulky Kilowog (Michael Clarke Duncan), though the training mainly consists of Kilowog slapping Hal around. Kilowog tests Hal by creating a sun construct with his ring that nearly sucks Hal into it. Kilowog states the construct has the gravitational pull of the average sun. If Kilowog also simulated the heat of the average sun, that would make this throwaway training move one of the strongest feats of power displayed in a live-action superhero film so far.
The comics' Green Lanterns are known for their over-the-top abilities. Hal once recreated his hometown Coast City after it and its citizens were destroyed. He also recreated all of the people, giving them personalities based on Jordan's memories of them.
A Green Lantern's power is as strong as their will and creativity. Kilowog was capable of creating a fully formed sun with its own gravitational field in moments. Therefore, it's possible Kilowog could increase the size of his pseudo-sun and accelerate it through its life cycle to become a black hole. The average sun's gravitational pull pales in comparison to a black hole, meaning Hal would have been swallowed up in an instant, which would've been a powerful weapon against Parallax.
Of course, creating something like a black hole is no easy task, even for a Green Lantern. The amount of willpower needed to simulate the gravitational power of a black hole would likely take a lot out of most Green Lanterns who attempted it. Kilowog is known to be a powerful member of the Corp, so his sun construct evolving into a black hole isn't impossible (given it reached the right size).
However, it's clear the movie didn't know just how much power it gave Kilowog at that moment. If elite Green Lanterns can just create suns at will, then the squad of Lanterns that went after Parallax could have incinerated him with their sun constructs. Hal only needed the Earth's sun to roast Parallax, which is nowhere near the largest star in the galaxy.
The only thing better than a green power ring is a yellow power ring, at least according to Sinestro (Mark Strong), who believes fear is stronger than will. To an extent, he is correct, as Green Lanterns and the green energy spectrum of will had a universal weakness to the yellow energy spectrum of fear (though they later found a workaround by conquering their own fears). Although Sinestro never did get to show off the power of his ring in a sequel, his brief moment of taking off the Green Lantern ring and putting on the yellow one was enough to show there's a difference in power.
Sinestro trembled from the might of fear compared to will as he put on the ring. If Kilowog can make a perfect replica of the sun with his ring, imagine what Sinestro can do with a ring powered by fear. Parallax, though the main baddy of the movie, wasn't all that impressive in terms of showing off powerful attacks. Sinestro, on the other hand, has the ability and training to master the power of fear. In an alternate timeline where a Green Lantern sequel was made, Sinestro would have a strength that might even put Thanos to shame.