Very cool, the idea of using watermelons to defeat fire monsters is perfect for summer. The mechanics of the watermelons are very well integrated, they serve for everything! as a weapon, as ammunition and to recover life. I had problems defeating the big fireball, I had to go back several times to buy more watermelons and it interrupts the rhythm of the game a bit, it would be nice to make it a little easier to defeat. I ended up spending all the gems on upgrades and ran out of gems to buy more watermelons. Partly because the way you buy items is just too much fun!
In general it is a very original and fun game, congratulations!