In the last decade, time-domain surveys have dramatically enhanced our understanding of stellar evolutionary pathways by providing accurate measurements of the physical parameters of many stars. Despite these advancements, significant gaps remain in our understanding of how massive stars conclude their life cycles and the details of their final evolutionary stages. For instance, what experiences do red supergiants undergo in the months to years before their explosions? What are the origins of the pre-explosion outbursts in interaction-powered supernovae, and how can these inform our understanding of their progenitors? Can Type Ia supernovae result from helium-shell detonations? Is there a continuum among stripped-envelope supernovae?In this dissertation, I will present progress on these topics through studies of five supernovae, including SN~2018cuf, SN~2023ixf, SN~2016dsg, SN~2022crv, and SN~2023fyq. Utilizing well-sampled photometric and spectroscopic data, alongside detailed hydrodynamic modeling, I have placed strong constraints on the progenitors of these supernovae. Remarkably, my findings suggest multiple mechanisms may be responsible for the dense circumstellar materials around Type II supernovae; some peculiar thermonuclear supernovae likely originate from thick helium-shell detonations; there is indeed a continuum between Type IIb and Type Ib supernovae; and a promising progenitor channel for Type Ibn supernovae involves a binary system with a compact object companion, capable of producing long-standing, bright pre-explosion emissions
