Gotham: 10 Villains That Should Appear In Season 4

9. Harley Quinn

Even though it's yet to be confirmed if Jerome is, in fact, the venerable Clown Prince of Crime (he very obviously is, let's be honest), it's clear that Gotham has found its Joker in that character. It is, however, yet to find its Harley, and while speculation has run rampant as to who the show's Harleen could actually be (some say it's Barbara, others Leslie), the true bearer of the mantle most likely belongs to the most unlikeliest of sources - a fleeting cameo in the season three finale.

Prior to the third season's conclusion David Mazouz had hinted that Harley would in fact be making an appearance in the finale, only for her inclusion to be, well, kind of obscure. Fans have speculated as to who Harley could've possibly been, but one of the more interesting theories revolves around a throwaway line given when Bullock arrested the Tetch-infested Gordon on the Gotham subway.

Inverse in particular made note of a specific New Yorker caught up in the bustle of Jim's arrest, and how they - much like the Quinn of the comics would - reacted with particular nonchalance towards the advancing officers, complete with the classic Quinn-twang.

Other theories have noted that the girl Bruce rescued at the end of the season could also be a Harley in waiting. Given just how far people are reaching for explanations however, it's more than likely that Harley - although not shown in the new trailer - could be making an appearance later than we all initially expected.