What's the fastest enemy in Tower Blitz?

Could you tell me, what is the swiftest adversary in the game Tower Blitz? I'm particularly intrigued to know which enemy poses the greatest challenge due to its speed, making it difficult for players to anticipate and counter its attacks. Understanding the speed of different enemies is crucial for devising effective strategies and ensuring victory in the game. So, what is the fastest enemy players need to be wary of in Tower Blitz?