  Curvatons are light (compared to the Hubble scale during inflation) spectator
fields during inflation that potentially contribute to adiabatic curvature
perturbations post-inflation. They can alter CMB observables such as the
spectral index $n_s$, the tensor-to-scalar ratio $r$, and the local
non-Gaussianity $\;f_{\rm NL}^{\rm (loc)}$. We systematically explore the
observable space of a curvaton with a quadratic potential. We find that when
the underlying inflation model does not satisfy the $n_s$ and $r$ observational
constraints but can be made viable with a significant contribution from what we
call a savior curvaton, a large $\;f_{\rm NL}^{\rm (loc)}$ is inevitable. On
the other hand, when the underlying inflation model already satisfies the $n_s$
and $r$ observational constraints, so significant curvaton contribution is
forbidden, a large $\;f_{\rm NL}^{\rm (loc)}$ is possible in the exceptional
case when the isocurvature fluctuation in the curvaton fluid is much greater
than the global curvature fluctuation.
