Question: What was the liquid in the big containers that Harley Quinn and Joker jumped in?
Answer: The same unknown acid/chemical combination that created the Joker in the first place.
Question: Near the end of the movie, how did the younger brother make it through the checkpoint in a stolen car? The cops would have run the license plate, no?
Answer: When they bought the car they told the store owner not to report it stolen until Friday.
Question: Why are the officers wearing dress blues in the beginning of the movie? The replacement commander of the 110th has a chest full of ribbons...The black military police officer at the command center. Everyday military officers would be wearing Class A's or fatigues.
Answer: Although it's technically a mistake, it is common in films to show military officers in dress uniforms with medals and ribbons to show that particular soldiers are important. A layperson may not know military uniform protocols but they can certainly tell that dress uniforms with a lot of medals signifies high rank at a glance.
Question: How much time has passed between the events of the first film and this film? Since pretty much half of the White House was destroyed in the first film, wouldn't it have taken some time to rebuild that section of the White House?
Answer: About a year has passed.
Answer: Once she saw the gun and knew how crazy the game was, she formed an idea that someone's would get shot and believed that it would be her.