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High precision astrometry has entered a Golden Age, ushered in by the Gaia mission and surely culminating in the clearest 3D picture of the Milky Way to-date. The Gaia satellite has been revolutionary in many ways and yet, as a relatively small telescope, it is fundamentally limited in its study of both faint and crowded sources. The MCAO Assisted Visible Imager and Spectrograph (MAVIS) is an instrument being designed for the Very Large Telescope Adaptive Optics Facility. Equipped with MAVIS, the VLT will be the only 8m-class telescope, ground-based or otherwise, to operate at its diffraction limit ($\sim0.02$~ arcseconds) in the optical (550 nm). Designed with astrometry in mind, MAVIS must deliver precision astrometry at the 150 micro-arcsecond level, with a goal of 50 micro-arcseconds, the same requirement as the 39~m Extremely Large Telescope. To verify this requirement will be met, we have created the MAVIS Image Simulator (MAVISIM), an image simulating tool to explore MAVIS science cases ranging from stellar to extra-galactic science. MAVISIM accounts for three major errors introduced by adaptive optics, including PSF field variability, along with imager and detector characteristics. In this first test of MAVISIM, we have investigated both the astrometric capabilities of MAVIS and a key science case for the instrument, the presence of intermediate mass black holes (IMBHs) in globular clusters. In this proceedings I will present exciting results from MAVISIM showing that MAVIS will: i) meet its astrometric requirements and ii) be able to detect the kinematic signature of a central 1500 solar mass IMBH in the crowded central region of NGC 3201.
