Ultra-diffuse galaxies (UDGs) have been one of the latest hypes in the extragalactic community. Although discovered a few decades ago, only recently we have had the opportunity to start grasping their nature thanks to deep photometric observations and, more challengingly, spectroscopic ones. From different properties ranging from their dark matter content, GC counts, stellar populations and dynamics, the current understanding is that UDGs are a mixed-bag of puffed up dwarf-like galaxies and failed ancient halos. However, which channel dominates, whether a particular stellar mass or environment has a saying on this nature, is still to be seen. In this talk I will present the largest spectroscopic sample of UDGs to date, which can provide clues on the formation channels from the analysis of the stellar population and kinematic properties. I consists of UDGs in the field, groups and clusters, thus allows us to investigate whether environment plays a role in shaping UDGs. Moreover, I will compare this set of spectroscopic UDGs with different cosmological simulations, to further elucidate whether a particular UDG is simply a puffed up dwarf or a failed ancient halos.