Were you expecting anything else? The silliest of silly games is impossible to beat because a familiar friend has gone villain and acts as the final boss. He's sick and tired of letting little Flappy fly around in what is clearly his world. Die bird, die.
The video is obviously but wonderfully doctored by the guys at pipocaVFX but it's pretty perfect. If you're an impatient type, fast forward to around the one minute mark to get right to the end where level 999 starts.