Observational properties derived from the bolometric LCs and spectra of the SN sample. Top left: Distribution of the peak luminosity L_M as a function of the ⁵⁶Ni mass estimated from the radioactive tail fit. The trend line is obtained through a linear regression log₁₀L_M-log₁₀M_Ni; the correlation is highly significant (p-value ≪ 0.01 and Pearson coefficient of 0.89). Bottom left: Distribution of t_f^* versus the ⁵⁶Ni mass for the same SN sample. Top right: pEWs as a function of expansion velocities for the Hα and Fe II lines, for the SNe with available data. The color and shape of the markers follow the top legend, while the marker border indicates the line type according to the internal legend. Bottom right: Same as the top-right panel, but for the Hβ and Ba II lines.