2014 MU69 [wikipedia.org], which New Horizons will fly by on January 1, 2019, appears to have an elongated shape or may be comprised of two objects [earthsky.org]:
Based on the occultation data, 2014 MU69 definitely appears to have an odd shape. In a press release, NASA officials said that it's either football shaped or a type of object called a contact binary. The size of MU69 or its components also can be determined from these data. It appears to be no more than 20 miles (30 km) long, or, if a binary, each about 9-12 miles (15-20 km) in diameter.
By comparison, Comet 67P/Churyumov–Gerasimenko [wikipedia.org] consists of a large lobe measuring about 4.1 × 3.3 × 1.8 km and a small lobe of about 2.6 × 2.3 × 1.8 km.