Discovery of the extremely luminous supernova SN2006gy has demonstrated that some of those events produce an order of magnitude more visible photons than other, already powerful explosions. I discuss models that were invoked earlier to explain unusual properties of other powerful supernovae with narrow emission lines in their spectra. Spectra and light curves for them can be explained only when a huge mass on the order of Msun and more is ejected within years before the observed explosion. A concrete (pulsational pair-instability) mechanism for these multiple supernova explosions has been proposed recently in our paper with S.Woosley and A.Heger to explain SN2006gy.