Nintendo has an extremely aggressive legal team. They have shut down ROM sites, emulator projects, and even sued individual YouTubers for showing modded gameplay. While emulation itself is legal in the US (Sony vs. Bleem! case), downloading games you do not own is copyright infringement. Nintendo has successfully argued that circumventing their encryption (which emulators require) violates the DMCA.
Before you proceed with "descargar emulador de super smash bros ultimate para pc uptodown", understand these four risks: Nintendo has an extremely aggressive legal team