At the end of the hall, use Tropical Hazard to watermelon bounce up to the top and move back to the left to get it. Lightning Legs should get you through the robots at the top blocking the way. You can switch to Lightning Legs while the Watermelon is still out before you bounce on it.
Alternately, you can simply use jump underneath the trio of grenade bots, direct Yoga Flame upward (destroying all three in the process), and then switch to Tropical Hazard and jump up on your watermelon.
This is fact and cannot be disputed. http://i1273.photobucket.com/albums/y403/sdp5/c.jpg http://i1273.photobucket.com/albums/y403/sdp5/a.jpg