This Most Wanted mission will become available near the end of the game after returning to the Clock Tower to shut down the computers.
This short side-mission takes place entirely on the small island in the centre of the city with the Lady of Gotham statue on it. When you arrive on the island you’ll find a preacher within a chain-linked fence giving a sermon to a large group of thugs in a small pit-type area below. As soon as you arrive a short scene will play and a timer will appear.
To complete the side-mission, we need to beat up all of the enemies within the time limit and then using our Remote Electrical Charge Gadget to disable the generators below the preacher’s platform. We’ll then need to use our Batclaw to grapple up and enter the small chain-linked area via a hatch on the outside.
The fight itself is a little tricky due to the time constraint and it consists of 25 Thugs (a couple of whom have knives) and two weapons crates which you’ll need to keep an eye on throughout the fight.
As soon as the fight is over, you have disabled the generators and hopped into the cage, a scene will play to end it.
Save the sacrificial victim and lock up the executioner in GCPD.