  We investigate two extensions of the standard model that include particle
dark matter candidates: the Next-to-Two Higgs Doublet Model and the
Next-to-minimal Supersymmetric Standard Model. These models feature a
non-Standard Model like CP-even scalar with a sub-TeV mass, denoted by $H_2$,
among other particles. At a 13 TeV proton-proton collider, the primary
production channel for such scalars is via the fusion of a pair of gluons.
Subsequently, these scalars can decay invisibly into a pair of dark matter
candidates, which can be dominant. In the supersymmetric model, it is possible
for the Lightest Supersymmetric Particle (LSP) and Next-to Lightest
Supersymmetric Particle (NLSP) to be mass degenerate, leading to
quasi-invisible $H_2$ decays to LSP+NLSP and NLSP+NLSP. We present the
predictions of both models for this challenging scenario while ensuring
compatibility with recent experimental constraints.
