In LEGO Batman Episode 2, Chapter 1 (AKA Power Crazed Penguin: There She Goes Again), start by plugging in the Invincibility cheat  in the in-game cheats menu: WYD5CP.

Then, trawl the level and get rid of the enemies so you can then walk around freely, looking for bonus content. There are ten minikits to find/assemble. Here's how you find the first three!

  1. Location: green slime to the left. Action: Put the LEGO pieces together, pull the lever and go through the underwater gate to retrieve the mini-kit.
     
  2. There are three silver containers in this level. Bust them all and grab the carrot inside to get the second mini-kit.
     
  3. There's a garage on the left from the starting point. Rebuild the LEGO pieces in front of the garage to build the lever that opens the garage door, then rebuild the car inside. Finally use a strong character (maybe a SWAT Officer - the cheat code is: HTF114) to move the car over to the other side and shift the block obstructing the other garage door, then park the car inside.