Nuclear star clusters are the densest stellar systems in the Universe with masses of 10^6-10^7 solar masses and half light radius of 2-5 pc. They are found in ~70% of galaxies across the Hubble sequence and are known to co-exist with black holes, as in the Milky Way. Some of the most massive globular clusters in our galaxy are thought to be the tidally stripped nuclei of disrupted galaxies. In this context, M54 - located in the densest region of the Sagittarius stream at 27.4 kpc- is an ideal target to study the still unknown connection between nuclear and globular clusters. I will present a deep study of M54 based on a large MUSE data set covering ~2.5Reff, including the stellar and kinematics characterization of thousands of individual member stars where we identified at least three stellar populations with clear kinematic differences between them. Furthermore, I will show the results of the application of discrete Jeans dynamical modeling on this data and how this compares with the resolved study. This work motivated us to perform a deep study of Omega Centauri, the most massive and complex galactic globular cluster, presumed to be a stripped nucleus. In this talk, I will show the first results of this new collaboration project.