I have done a little research by way of reading the rules (always a good idea) and it turns out that the Batman Miniature Game has a few layers of complexity to it that only come to light by reading up on some of the Special Traits. I introduce you to the Circus Gang.
One of the models that I have purchased is the Ringmaster. (This is not my painting - found it on the internet)
One of his Personal Traits is Elite (Circus Gang). A little reading shows me that I can only have one Elite per Crew unless I hire the the Elite Boss for that gang. The Elite Boss for the Circus Gang is none other than Mr Hammer.
Mr Hammer has Elite Boss (Circus Gang) listed as one of his Personal Traits. However Mr Hammer is also a Sidekick. Only one Sidekick is allowed per Crew so you have to choose between Mr Hammer and the wonderful Harley Quinn (either version). So this starts to become a bit of a sub-crew within a crew. Who else is in the Circus Gang I hear you ask? Good question. Well the Master of Ceremonies is the answer.
This does seem to make a little sense as the two Henchmen are dressed in a similar fashion wearing Catchers Gear.
So there is the option to play the Circus Gang within the Crew by bringing Mr Hammer, the Ringmaster and also the Master of Ceremonies. I will have to do a bit more research to fully understand the benefits but there appears to be be a deliberate move to group the three of these guys together in opposition to playing Harley Quinn.