Instructions
Load "Super Scribblenauts" to the main menu. Tap "Custom Levels."
Tap any of the empty slots to begin creating a new level.
Tap one of the backgrounds to set it as your custom level's background. Tap the notebook in the corner to edit the name of your level. Tap "OK" to continue.
Tap "Playground" as your level type. You must have it set to this option to have it as your title screen. Tap "OK."
Add items to your level as desired. This works the same way as a regular level. Tap the icon of a floppy disk to save your level. Tap the left arrow to go back, followed by "Yes" to set it as your playground, unlocking the merit.