This video shows you how to get the hidden melon in level 2 (5-2).
To get the melon send a bird off to the far right side of the level past the LAST umbrella and blow up the TNT. Important, the TNT is NOT visible on all devices (it’s off the screen), but if you hit it you will likely see the explosion. Once you do hit it the explosion will cause a labeled crate to swing down on a chain. Break the chain or the crate to find the melon.
Note, based on a lot of comments we’ve received this melon seems to be the one people are missing most often (e.g. “I only have 14/15 of melons, but I swear I’ve got them all!!! What gives?”). A big thanks to AMslimfordy for spotting this. His advice has a helped a lot of people get all 15 melons.