2003 UZ413 is in a 2:3 resonance with Neptune, which means that when it makes two revolutions around the Sun, Neptune makes exactly three.
The object rotates very fast. In fact, with a period of about 4.13 hours, it is the fastest rotator known in the Kuiper belt after Haumea.
The size of 2003 UZ413 is not known, but a reasonable estimate is around 600 kilometres (370 mi).[g] This estimate puts it on the borderline between the 2nd ("highly likely") and 3rd ("likely") classes in astronomer Michael Brown's five-level system of classifying the probability that an object is a dwarf planet, although he himself only estimates its size at 536 km, therefore more towards the lower end of the "likely" group.
Given its rapid rotation, it must have a density higher than 0.72 g/cm3. Stable Jacobi ellipsoids with an axis ratio of a/b ≥ 1.13±0.03, as implied by its light-curve amplitude of Δm = 0.13±0.03, exist for densities in the range of 2.29−3.00 g/cm3. The Johnston's Archive settles on 2.64 g/cm3, the centre of the latter range; for a 600 km equivalent spheroid body, this would equate to a mass of approximately 3.0×1020 kg. The relatively high estimated density (in stark contrast to many similarly sized TNOs)  increases the chance that the object has no internal porosity and has collapsed into hydrostatic equilibrium (a requirement of being certified as a Dwarf Planet), but confirmation of this hypothesis requires observations to refine the size and light curve details, preferably with determination of the orbit of any satellite that may exist.
In visible light, this object is neutral or slightly red in color and has a flat, featureless reflectance spectrum.
^Buie page actually says 3:2 resonance... thus, also "Plutino"
^using assumed albedo of 0.25 to 0.05, and 4.3 absolute magnitude as per JPL/MPC; using 4.38 magnitude as per Perna et al (2010) gives a ~3.3% smaller estimate, i.e. 356-791 km
^W.M. Grundy, K.S. Noll, M.W. Buie, S.D. Benecchi, D. Ragozzine & H.G. Roe, 'The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK126)', Icarus(forthcoming, available online 30 March 2019) DOI: 10.1016/j.icarus.2018.12.037,