Massive stars have been known to end their lives violently for almost a century, but the extremes of this process have become appreciated only recently: rare classes of "superluminous" supernovae are hundreds of times more luminous than other SNe, and long-duration gamma-ray bursts fleetingly outshine the brightest quasars by orders of magnitude. Their immense luminosities make these events easily detectable from great distance, from which they can serve as probes of the high-redshifts IGM, ISM, and rate and sites of cosmic star-formation. However, employing them as tools in this way requires a thorough understanding of how varying conditions such as metallicity may favor or disfavor their production in different environments. I will discuss two large surveys I am leading to study the connection between extreme transients and their galaxy environments: SHOALS, a multi-observatory effort to examine the impact of galaxy evolution on the GRB rate and host population across cosmic history, as well as the PTF superluminous-supernova host project at Keck and Palomar. Extreme transients will be discovered at a much wider range of distances and greater numbers in the coming era of all-sky synoptic surveys, and studies of these events and their environments with existing and upcoming facilities will prove invaluable for understanding the composition and evolution of dwarf galaxies, the history of the early universe, and theories of massive-stellar evolution and variations in the IMF.
