IMO a unicorn is a full stack developer that also has design / marketing knowledge. the thing is about these guys, is most of them are savvy enough to create their own products, apps or startups and if you do find them it is a matter of time before they break off and do something on their own.
I don't think that's always the case. I ran my own company for years but honestly running a company gets exhausting. After years of doing it I came to the realization that what I really like doing is growing companies, not running them.
Once I realized that, it was an easy transition back to being an in-house marketer.