Legal disclaimer: Satire/Parody. This post is a joke. Do not break the law, especially because you read some dumb blog online.
You should pirate Undertale. Its a decade old, and still sells a ton of merch, meaning its creator is not at financial risk. It got DRM-free releases, meaning pirating it is fairly trivial. But its not entirely non-trivial, you will learn a lot about piracy by pirating Undertale. Its also a small game in terms of file size: if you make a misfire, you won’t lose too much in terms of download time. Just watch out for viruses! It’s a good game, too. It’s a popular game, its an influential game, its one of the Games You Should Play TM. But if you don’t want to play it, the game starts quickly, you can easily boot it up to check you did it correctly and transfer your new skills to pirating something you want to play.