You decided to open a portal to either Undertale or Deltarune, however the only issue now was which one to travel to? While both had a vast cast of characters there were so many options, you also figured you could go to au's of either game as well, same with the different routes. Or the different chapters of Deltarune. 

Another thought was going to a version of Undertale or deltarune that didn't follow the games story or continuity.