To unlock the jump pad that gives you access to the moon levels, you need to first complete the regular sixteen levels. Once done, Grannie will give you permission to access the moon. Note: Completing the secret levels does not count towards unlocking the moon.
Unlock the following power-ups in Grannie's Attic by collecting the corresponding number of golden diamonds:
POWER-UP - GOLDEN DIAMONDS Extended Hover - Collect 1200 Golden Diamonds Power-shot - Collect 800 Golden Diamonds Vertical Boost - Collect 1600 Golden Diamonds Moon Level - Beat the first 16 Levels. Play as Grannie - All 2000 Gold Diamonds and 40 Water Sprites Collected.
After collecting all the 2000 Diamonds and 40 Water Sprites in the game, press the L button on the title Screen to switch to Grannie. After that, start the game. Grannie has all of the available power-ups in the game to use at once.