Ford Mustang Boss 351
The Mustang Boss 351 was the next generation of the famous pony car. Unfortunately, to the dismay of enthusiasts, the Boss 302 and Boss 429 versions were discontinued. There were only 1800 examples of the Boss 351 put into production. The car was fairly rare at the time and has maintained that rarity today as a result (via Car & Driver).
The Boss 351 was a letdown for many loyalists who hoped the car would be as fun as the first generation. The styling of the second-generation Mustang is often considered one of the ugliest in the history of the model overall.