Batman Arkham City Plot Confusion (spoilers ahead)

So, i just beat arkham city, and i don't quite get it. what was the purpose of the joker using clayface as a double? why didnt he just use the cure on himself for real instead of just holding on to it for most of the game? I just feel like the whole clayface body double thing was completely pointless

Joker didn't get the cure at first. The leader of the League of Assassins daughter (can't remember her name) stole the cure from Harley before she can get it from the Joker. So then Joker used Clayface to make Batman think he had been cured to lure Batman there because Joker thought he still had the cure. Not sure about the using Clayface part but the rest is accurate.Raikin1

why didnt anyone question where bruce wayne was at the end? everyone saw him get hauled off to AC, but after protocol 10, do they think he was killed during all the chaos?gearsofhalogeek