Hall of Doom
You can reach the Hall of Doom from the Hall of Justice. Look for this silver statue to the right of the entrance and use a demolition character to destroy it. Then use a big character to break through the cracked floor, opening a tunnel to the new area.
Gold Brick #1
You can find Mister Mxyzptlk in the swamp. Talk to him to start a fight against Lobo. Just land a few hits in between battles with minions to end the tussle and receive your reward.
Gold Brick #2
Return to Mxyzptlk to start a second quest. This time, he'll need your help fending off some birds. Take out all 15 for another brick.
Gold Brick #3
Now the Penguin will take Mxyzptlk's place. Talk to him to help escort his three penguins. The first is behind a magnetic door, the second is past a silver axe, and the third is behind an electric panel. Use the appropriate characters to open the paths and lead the penguins back to their boss. You'll get a Gold Brick for it.
Gold Brick #4
Now Poison Ivy is found in the swamp. She needs your help getting a little "closer" to Swamp Thing. Use a frost or shield character to put out the flames and guide her to him, and she'll reward you with a brick.
Gold Brick #5
Return to Poison Ivy and Swamp Thing to find them in a lover's spat; they need a special concoction to solve the problem. Use a magnetic character on the lab set (left magnet, switch, right magnet) to create the potion. Return it to Poison Ivy for another Gold Brick.
Gold Brick #6
You can find Batgirl inside the hall proper; she needs help finding some blueprints. To get them, you'll have to find 5 pieces inside 5 filing cabinets. There are two on the left side of the room, and three on the right. Bust them all up to complete the quest and earn a brick.
Gold Brick #7
Next up in the hall is Harley Quinn, and she needs help from a crash test dummy. To help her, create a custom character using the Crash Test Dummy head and torso. Return to Harley in this getup to be rewarded with a brick.
Gold Brick #8
Harley has another quest for you: therapy (no, really). To help, simply talk to the three characters on the ground floor and lead them back to Harley. This simple act earns you a Gold Brick.
Gold Brick #9
In the swamp area are five dragonflies (sometimes they glitch out and not all five appear; reset the game to fix this). Shoot one to start a timer, then shoot the others before it runs out to earn a brick.
Gold Brick #10
There are five targets inside the hall proper: above the entrance, behind the left stairs, above the central alcove, above the right balcony, and on the far right side of the room. Shoot them all to shut down a laser gate on the right balcony. Now use a laser character to melt the gold statue beyond, earning yourself a Gold Brick.