It depends. Sometimes movies or stories labeled as ATL might be based on real events, but they could also have fictional elements added for entertainment purposes.
The location of the ATL Comic Convention isn't always the same. Sometimes it's at a convention center, and other times it could be at a larger event space. To be sure, I'd recommend looking at their official announcements or social media pages for the exact spot.
The 'Undertale Online 20 Minit Story' might be a condensed version of the rich Undertale experience. In Undertale, the story often revolves around the choices the player makes. So in this 20 - minute story, it could be that players are presented with a series of quick decisions that impact the outcome. It might start with the player's character entering a new area in the online Undertale world. They could meet new and familiar characters, engage in battles or dialogues. And all of these interactions within the 20 minutes could lead to different endings depending on the choices made.
Well, in the 'minit game story', it might be a story of a group of friends who get trapped in a mysterious world. They then have to find a way to work together to escape. They might encounter strange creatures and hidden treasures along the way. They need to use their unique skills, like one is good at climbing, another at finding clues, to get out of that world.