anything mysterious, dangerous, unusual, unexpected, confusing, or sketchy
synonomus with "sketchy"
when you see a man walking around at midnight, you might say that he is a darkhorse, or that the situation is darkhorse because that is an unusual event
basically this word can be used in any form
ex. "that guy is a major darkhorse" (that guy is mysterious)
ex. "that game was so darkhorse" (that game was confusing)
ex. "darkhorse!" (exclaiming that something is sketchy)