- You have a seed phrase where the first 6 words and their order are known. For example, you have: crawl vanish secret like rail blush <and 18 unknown words missing>
- You have a list of 26 words which are valid out of the 24, but I'm not sure what this means. Is there a passphrase which extends the 24 word-phrase, or does your 26 word-list contain the 18 other words which you need to complete the 24 word-phrase?
Even without a passphrase, if you know the exact 18 words but not their order, you would still need to search through 18! (6,402,373,705,728,000) permutations to cover the entire space of possible seed phrases. Even with immense computing power capable of searching 1 million seed phrases per second, it would take about 6.4 billion seconds to complete, or roughly 205 years of continuous operation. And that's your best case scenario.
There would be approximately 1,216,451,004,088,320,000 possible combinations, because there are 20 words to combine to form permutations of 18 words.