WST will provide an unprecedented spectroscopic characterization of transient and timevariable phenomena. WST’s IFS and MOS will collect medium-resolution (R~5-7k) spectra of up to 10,000 transient phenomena every night, including supernovae (SNe), active galactic nuclei, tidal disruption events (TDEs), gamma-ray-bursts (GRBs), and fast radio bursts (FRBs), among others. Serendipitous transient observations at random phase will be collected while surveying distant galaxies, while intentional observations will be taken in response to alert brokers (e.g., Rubin/LSST).