Do not trust random YouTube links. The only official source is the "Dimension Jumpers" Discord server (links available via their legitimate Twitter account @MultiverseMario). Once inside, navigate to the #beta-download channel.
Because the multiverse is unstable, random "Glitch Storms" occur. During these, the screen distorts like a corrupted VHS tape. Gravity inverts, coins turn into enemies, and checkpoints vanish. This is brutally difficult but exhilarating. Mario Multiverse Game Download Beta
Because the project exists in a legal grey area, you will not find it on the App Store, Google Play, or Steam. Instead, the development team distributes it via encrypted Discord servers and archive.org mirrors. Follow this step-by-step guide: Do not trust random YouTube links