That Pokemon you always wanted, but could never catch.

[Xannidel]

For me growing up on Red and Blue, I always wanted a Chansey and Kangaskhan from the Safari Zone but wouldn't you believe it that every encounter with EITHER of them resulted in then running away before I could even throw one rock!?

After that I cared less about getter rare pokemon because the pokemon I found at a better catch/encounter rate did the job for beating the gym leaders and the elite 4.