[hueving]

It's effectively gambling on the future of various currencies. It's no different than day trading or forex at this point so it's not really a good way to get 'passive income' since it can very easily turn into 'passive losses'.

[koonsolo]

Most suggestions here are gambling. Things that are low risk don't give much return. If you want it to be passive, you either need to have a lot of money/time or take risk and be lucky.