From the pages of Legion of Super-Heroes, Cosmic Boy features the titular legionnaire and his girlfriend Night Girl, as they go on a vacation in the 20th century. Their vacation is quickly hijacked by the Legends event, and by one of their greatest foes.
For more about the character, see the Legion of Super-Heroes Founders character sheet.
Cosmic Boy provides examples of:
- After the End: When they realize they're not helping anything and that changes to the past mean their own time is likely changed as well they try to return home where at least they could ask Brainiac's opinion on what's happened, only for their trip to be hijacked by the Time Trapper who takes them to the end of time.
- Alternate Timeline: Rokk has been in the past before, but realizes he somehow made it to a past where his many previous visits never took place and people have a bizarrely negative view of superheroes.
- Badass Boast: The Time Trapper has some decent bragging:Time Trapper: Call it a room if you will. It's simply a little section of my personal playground, here at the end of time. Remember, the very existence of this place is proof of my ultimate victory. In the end all things will be reduced to what I permit them to be, dust.
- The Bad Guy Wins: Rokk and Lydda do nothing to prevent further tampering with time or correct what's already been done and barely escape the villain responsible. Even that escape was orchestrated by the villain, and they'd never have found out who was responsible if the villain didn't grab them in order to gloat and then send them home just so that they can spend the rest of their lives knowing they're going to be erased from history.
- Battle Couple: Rokk and Lydda are essentially a superhero couple on vacation, who discover that the timeline is being messed with and work to try and fix it by fighting those responsible.
- Big Applesauce: Despite the fact that New York remaining the same cultural center it is in the real world making no sense in the DCU due to Gotham and Metropolis's histories, locations and sizes the Big Apple carries on its grand tradition of being an important historical city in the same vein as the real one every time every time a writer decides to locate a DCU story there.
- Butterfly of Doom: Lydda is concerned she and Rokk are the source of the major rewrites to history, he discounts this theory since their mode of time travel has been used safely many times before but she points out that things were different this time and something's obviously gone wrong, even if it wasn't them she figures they should fix it.
- Fan of the Past: Cos' interest in the 20th century allows him to notice right away that things are not right when he's trying to vacation then.
- Fantasy Metals: When trying to escape back to their time Lydda wonders if the wall between her and Rokk is made of inertron, the hardest metal in the DCU.
- Faux Affably Evil: Time Trapper may laugh and let them "escape" but he pretty much brought them to the end of the universe to entertain himself with their struggles and rather them them actually escaping it's made explicit he placed them back in their own time rather than them driving themselves there. He's also in the process of erasing history and has no intent of stopping or slowing down when he reaches their time period.
- Kid from the Future: It's not made explicit but Rokk helps out and is helped in turn by his astronaut ancestor Jason Krinnski, who doesn't have kids yet but obviously will need to for Rokk and his family to exist.
- Shout-Out: One of the drones attacking Rokk on Time Trapper's orders is clearly a thinly veiled Storm Trooper.
- Timeline-Altering MacGuffin: Rokk figures out history, or at least records of it, have been altered very quickly and decides to be on the lookout for who, or what, is messing with time.
- Time Travel for Fun and Profit: Rokk and Lydda came to the 20th century on a vacation.
- Ungrateful Bastard: One of the clearest signs that history has been changed is the way the public reacts to heroes with distrust, hate and outright attacks.
- Weaksauce Weakness: Night Girl's already rather debilitating weakness to UV radiation is presented as a weakness to light in general making her use of her powers extremely limited in this book.
- What Beautiful Eyes!: According to this book the reason Lydda begged her father for superpowers was that she fell in love with Rokk's pretty blue eyes when she saw him during news reports and wanted to join the legion to be with him.