  We explore the ability of the high luminosity LHC to test models which can
explain the 750 GeV diphoton excess. We focus on a wide class of models where a
750 GeV singlet scalar couples to Standard Model gauge bosons and quarks, as
well as dark matter. Including both gluon and photon fusion production
mechanisms, we show that LHC searches in channels correlated with the diphoton
signal will be able to probe wide classes of diphoton models with $\mathcal{L}
\sim 3000\, \text{fb}^{-1}$ of data. Furthermore, models in which the scalar is
a portal to the dark sector can be cornered with as little as $\mathcal{L} \sim
30\, \text{fb}^{-1}$.
