Tetris Worlds is a strange GBA game and shouldn’t be confused with the corresponding console versions with the same name. The American version (GBA) only has Multi-Pak link mode whereas the European release supports both Single-Pak and Multi-Pak link.
Unfortunately, the overall Tetris experience is compromised quite a bit when playing head-to-head in the multiboot mode but still enjoyable because, hey, it is Tetris! Just weird how only EU players got this exclusive feature. Guessing it was a budget or time thing when it was released in America.