Neutrinos have been surprising us ever since the mankind took a glimpse of their elusive world. The notion of neutrinos being coupled to light and yet more elusive particles is intriguing. If the coupling of such hypothetical particles are large enough, they can dramatically affect cosmological observables such as BBN and CMB as well as supernova evolution. To be able to extract information from these cosmological and astrophysical observations, it is imperative to learn about possible new light particles coupled to the neutrinos via terrestrial experiments. After a short review of the effects in supernova and in the early universe, I will discuss how the new couplings can be probed by Coherent Elastic $\nu$ Nucleus Scattering (CE$\nu$NS) experiments and by exotic meson decay modes.