Stripped envelope supernovae are known to have progenitors that have lost their hydrogen outer layer as well as possibly also their helium layer, but recent evidence indicates that at least some interact at late times with hydrogen-rich material. In this talk, I will present the unusual superluminous supernova 2017ens (peak brightness of -21 mag) identified from the GREAT (GROND-ePESSTO-ATLAS) survey. A high quality spectroscopic dataset collected with WiFeS, NOT, Keck, NTT, VLT shows a blue featureless spectrum at early times, which evolves to a broad-lined Ic supernova that is spectroscopically similar to SN 1998bw. At late times, spectra are dominated by significant interaction showing strong Balmer lines and He I lines. In particular, in our intermediate resolution Xshooter spectrum we find very narrow emission and absorption H-alpha and H-beta lines with velocity widths of about 100 km/s, indicative of the presence of a very dense shell. This velocity is far slower than those present in Wolf-Rayet star winds, which implies its origin may come from the binary component or the progenitor could be a luminous blue variable star. Qualitatively speaking, to provide such massive circumstellar medium the progenitor must have erupted close to the explosion. We therefore propose that SN 2017ens is a candidate pulsational-pair instability, which may provide a precious link between superluminous supernova, broad-lined Ic and potentially pulsational-pair instability supernova.