  A diphoton excess with an invariant mass of about 750 GeV has been recently
reported by both ATLAS and CMS experiments at LHC. While the simplest
interpretation requires the resonant production of a 750 GeV (pseudo)scalar,
here we consider an alternative setup, with an additional heavy parent particle
which decays into a pair of 750 GeV resonances. This configuration improves the
agreement between the 8 TeV and 13 TeV data. Moreover, we include a dark matter
candidate in the form of a Majorana fermion which interacts through the 750 GeV
portal. The invisible decays of the light resonance help to suppress additional
decay channels into Standard Model particles in association with the diphoton
signal. We realise our hierarchical framework in the context of an effective
theory, and we analyse the diphoton signal as well as the consistency with
other LHC searches. We finally address the interplay of the LHC results with
the dark matter phenomenology, namely the compatibility with the relic density
abundance and the indirect detection bounds.
