Legion of Super-Heroes 18 (Jan 86) is a Crisis on Infinite Earths crossover, and, appropriately enough, Levitz, LaRocque and Mahlstedt make the Infinite Man the villain of the tale. I really liked this character when he debuted back in the 70s, but this was only his second appearance. The Infinite Man is simply too powerful to be an effective recurring villain, but was perfectly suited for this story.
As the tale opens, Rond Vidar discovers that Kid Psycho has died in the Crisis. Moreover, he discovers that the Legion itself has been participating in the events, but they have no memory of it. Rond shares his discovery with Brainiac 5, who is also suffering this memory loss, which might explain why he seemed to get over Supergirl's death so quickly.
All of the Legionnaires are affected, as we see at Kid Psycho's funeral. Element Lad, Shadow Lass and Mon-El are mourning him, but realize they have no idea of how he died.
While that is going on, other members of the team are on Takron-Galtos, the prison planet, which is being destroyed by a wave of anti-matter. This allows for a lot of minor villains to get cameos as they fight against the people who have come to rescue them.
Tellus winds up freeing Validus from the giant block of inertron he is being kept in. Validus gets Boomm Tubed away from the crumbling planet, which ought to be enough to let one know who is being that.
Working with Circadia Senius, Vidar and Brainiac 5 determine that the properties of the Time Beacon seem to be preventing the effects of the Crisis, and the very awareness of it, from taking hold in thhe 30th century. But their attempt to fix this situation winds up releasing the Infinite Man from the time stream in which they had trapped him the first time. I love the visuals for this character, and he looks even better this time around.
While it is never easy to defeat this guy, who is able to draw minions from any period of time, and move through it at will, Brainiac 5 gets the White Witch to cast a spell linking the Infinite Man to the power generated by the Crisis, pulling the time stream powers from his body. Jaxon Rugarth returns to his human form, though much later we will find out he has been left comatose. Without the Infinite Man unintentionally protecting the 30th century, the Crisis can now affect it.