Go to Millstone Mayhem as Diddy Kong. Lure the Krusha from the first screen back to the entrance. Stand on top of the entrance itself, and wait for the Krusha to walk towards you. Just before he reaches the entrance, slide down and hold the control stick left. If done correctly, Diddy will bounce off the Krusha's chest and back onto the entrance, resulting in both characters' animations getting stuck. As each bounce registers as a hit, you'll automatically rack up extra lives. The counter display stops at 99, but can go beyond that. Once you think you've gotten enough lives, let go of the control stick to return things back to normal.