  The development of the latest generation of Imaging Atmospheric Cherenkov
Telescopes (IACTs) over recent decades has led to the discovery of new extreme
astrophysical phenomena in the very-high-energy (VHE, E > 100 GeV) gamma-ray
regime. Time-domain and multi-messenger astronomy are inevitably connected to
the physics of transient VHE emitters, which show unexpected (and mostly
unpredictable) flaring or exploding episodes at different timescales. These
transients often share the physical processes responsible for the production of
the gamma-ray emission, through cosmic-ray acceleration, magnetic reconnection,
jet production and/or outflows, and shocks interactions. In this review, we
present an up-to-date overview of the VHE transients field, spanning from novae
to supernovae, neutrino counterparts or fast radio bursts, among others, and we
outline the expectations for future facilities.
