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With a central surface brightness of $\mu_0=29.3$ mag. per sq. arcsec, andhalf-light radius of $r_{\rm half}=3.1^{+0.9}_{-1.1}$~kpc, Andromeda XIX (AndXIX) is an extremely diffuse satellite of Andromeda. We present spectra for$\sim100$ red giant branch stars in this galaxy, plus 16 stars in a nearbystellar stream. With this exquisite dataset, we re-derive the properties of AndXIX, measuring a systemic velocity of $v_r=-109.0\pm1.6$ km/s and a velocitydispersion of $\sigma_v = 7.8^{+1.7}_{-1.5}$ km/s (higher than derived in ourprevious work). We marginally detect a velocity gradient along the major axisof ${\rm d}v/{\rm d}r = -2.1\pm1.8$ km/s kpc$^{-1}$. We find its mass-to-lightratio is higher than galaxies of comparable stellar mass ($[M/L]_{\rm half} =278^{+146}_{-198}M_\odot/L_\odot$), but its dynamics place it in a halo with asimilar total mass to these galaxies. This could suggest that And XIX is a"puffed up" dwarf galaxy, whose properties have been altered by tidalprocesses, similar to its Milky Way counterpart, Antlia II. For the nearbystream, we measure $v_r=-279.2\pm3.7$ km/s, and $\sigma_v=13.8^{+3.5}_{-2.6}$km/s. We measure its metallicity, and find it to be more metal rich than AndXIX, implying that the two features are unrelated. Finally, And XIX's dynamicaland structural properties imply it is a local analogue to ultra diffusegalaxies (UDGs). Its complex dynamics suggest that the masses of distant UDGsmeasured from velocity dispersions alone should be carefully interpreted

A detailed study of Andromeda XIX, an extreme local analogue of ultra diffuse galaxies