Underneath Ursula's unbelievably ugly umbrella unabashed underground urchins understandably urged Ursula's underwear's update, uselessly. "Uncouth undeserving usurpers!" Ursula uttered uncharitably. "Unhand ur uranium ultraviolet ukeleles! Umpires umbrate u!"
There are so many words starting with the letter "U", because of the prefix "un", but I'm sorry that I had to cheat with "ur" and "u". I think I used an incorrect definition of "umbrate", too. I wanted "shadow" as in "to haunt someone".