On Revenge of the King, if you go to Stage 2, there is a secret room with the word HAL spelled out. To find it, go to the area with the stone switch. When you hit the switch, and the blocks break, go to the left and press up. There should be a door there. When you go through, you will face a mini-boss. Beat him and continue to the right, Soon, you should get to a room with blocks spelling out HAL, along with an Invinsible Candy.