I'm honestly surprised that no one has yet mentioned the most obvious clue about Merrymaker being Dr. Meredith; his costume. He's dressed like a doctor form Europe in the Middle Ages/Renaissance, which was a dead giveaway to the man under a mask being a doctor. It's funny that people will over analyze his name and other factors, and miss such an obvious detail like that.
Another great issue from the team of Layman/Fabok. I'm really enjoying this run of Detective Comics!