In our previous work, we searched for superflares on different types of stars while focusing on G-type dwarfs using entire Kepler data to study statistical properties of the occurrence rate of superflares. Using these new data, as a by-product, we found 14 cases of superflare detection on 13 slowly rotating Sun-like stars with rotation periods of 24.5–44 days. This result supports the earlier conclusion by others that the Sun may possibly undergo a surprise superflare. Moreover, we found 12 and seven new cases of detection of exceptionally large amplitude superflares on six and four main sequence stars of G- and M-type, respectively. No large-amplitude flares were detected in A, F or K main sequence stars. Here we present preliminary analysis of these cases. The superflare detection, i.e., an estimation of flare energy, is based on a more accurate method compared to previous studies. We fit an exponential decay function to flare light curves and study the relation between e-folding decay time, τ, versus flare amplitude and flare energy. We find that for slowly rotating Sun-like stars, large values of τ correspond to small flare energies and small values of τcorrespond to high flare energies considered. Similarly, τ is large for small flare amplitudes and τ is small for large amplitudes considered. However, there is no clear relation between these parameters for large amplitude superflares in the main sequence G- and M-type stars, as we could not establish clear functional dependence between the parameters via standard fitting algorithms.