We report the results of our follow-up campaign of the peculiar supernova ASASSN-15no , based on optical data covering \sim 300 Â days of its evolution .
Initially the spectra show a pure blackbody continuum .
After few days , the HeI \lambda \lambda 5876 transition appears with a P-Cygni profile and an expansion velocity of about 8700 km s ^ { -1 } .
Fifty days after maximum , the spectrum shows signs typically seen in interacting supernovae .
A broad ( FWHM \sim 8000 km s ^ { -1 } ) H \alpha  becomes more prominent with time until \sim 150 days after maximum and quickly declines later on .
At these phases H \alpha  starts to show an intermediate component , which together with the blue pseudo-continuum are clues that the ejecta begin to interact with the CSM .
The spectra at the latest phases look very similar to the nebular spectra of stripped-envelope SNe .
The early part ( the first 40 days after maximum ) of the bolometric curve , which peaks at a luminosity intermediate between normal and superluminous supernovae , is well reproduced by a model in which the energy budget is essentially coming from ejecta recombination and ^ { 56 } Ni decay .
From the model we infer a mass of the ejecta M _ { ej } = 2.6 M _ { \odot } ; an initial radius of the photosphere R _ { 0 } = 2.1 \times 10 ^ { 14 } cm ; and an explosion energy E _ { expl } = 0.8 \times 10 ^ { 51 } erg .
A possible scenario involves a massive and extended H-poor shell lost by the progenitor star a few years before explosion .
The shell is hit , heated and accelerated by the supernova ejecta .
The accelerated shell+ejecta rapidly dilutes , unveiling the unperturbed supernova spectrum below .
The outer ejecta start to interact with a H-poor external CSM lost by the progenitor system about 9 – 90 years before the explosion .