A minor planet with the farthest closest approach to the Sun in the Solar System, this extreme TNO’s orbit was interpreted as evidence of Planet Nine.
Orbiting at a highly inclined 29 degrees to the plane of the Solar System, Makemake’s orbit lies far enough from Neptune to remain stable and free from perturbation from the ice giant.
Though not directly observed, Haumea is thought to be an ellipsoid world. In October 2017 astronomers announced the discovery of a ring system, the first around a trans-Neptunian object.
About the same size as Pluto, this dwarf planet and its small moon Dysnomia orbit three-times farther from the Sun. Its high-eccentricity orbit means it was likely scattered by Neptune.
Perhaps the most famous resident of the Belt, Pluto is the largest and most massive member. It is also the most studied, thanks to the New Horizons probe.
Sedna has an extreme orbit that ranges from 76 AU to over 900. While Planet Nine doesn’t explain Sedna’s orbit, it could provide the buffer that kept it from being ejected.