WARNING: The following article contains spoilers for Infinite Frontier #1 by Joshua Williamson, Xermanico, Romulo Fajardo Jr., and Tom Napolitano, on sale now.
Green Lantern Alan Scott just had a bit of revenge against an old enemy of his from "Zero Hour." His work alongside the Totality puts him on the forefront of preventing threats to the continuum of the new Infinite Frontier. But this new responsibility finally gave him a second shot at Extant, a villain responsible for killing members of the Justice Society of America and removing the temporal effects that kept them young well past the 1940s. To make that better, the fact that Alan stopped him while Extant was trying to pull the same stunt for a second time.
Extant is a very personal enemy for Alan. He was originally Hank Hall, better known as Hawk, but one from a dystopian future where he ruled the Earth as a tyrant named Monarch. Upon realizing that he held the power of both Hawk and Dove, Monarch shed his persona for a new one: Extant. He then went on a rampage throughout the timeline of the DCU, intent on changing time according to his whims. One of those whims put him on a collision course with the JSA that would prove disastrous for the team of heroes.
By that time, Extant had developed and mastered temporal abilities which he then used to full effect. Alan Scott watched as most of his teammates were killed before his eyes. Those that weren't were withered away into old men. Alan was the only one of them to survive the battle without physical injury, but the emotional scars still lingered. Not long after this, Alan stepped away from the spotlight as Kyle Rayner took over as DC's only active Lantern.
As a direct result of this, Extant is a deeply personal enemy for Alan. The villain resurfaced in Infinite Frontier #1, once again attempting to conquer time for himself. He was then promptly hit by a train created by Alan Scott's power ring. The surprise attack caught him off guard and ensured the Totality a swift victory.
Extant's actions in the past effectively ended the JSA, a part of Alan Scott's life that he held dear. He had to watch as the villain either murdered the rest of his friends or withered them into an age where they were essentially helpless. Extant didn't just hurt Alan, he robbed him and his friends of their identities.
In essence, Extant knocked the JSA off of a pedestal they put themselves on. Not one of arrogance, but the belief that they would stand firm in the face of any evil. Extant ruined that belief. He made what once seemed infallible fallible. So it's no surprise that Alan took a sense of satisfaction from personally defeating him.