Bip39-Standalone. The passphrase is just not chosen from your predefined list of 2048 words – it can be any word or phrase you choose. Anybody else who discovers the phrase can steal the bitcoins. It must be kept mystery, one example is it should not be typed into any website. https://bookmarkingfeed.com/story18579055/bip39-https-linktr-ee-bip39-5-simple-statements-about-bip39-mnemonic-explained