While accurate, the Standard Model remain incomplete, unable to explain phenomena such as dark matter. I investigate two extensions of the Standard Model: the two Higgs doublet model (2HDM) with an additional scalar (s) or pseudo-scalar (a) singlet. Assuming the Weakly Interacting Massive Particle (WIMP) model of dark matter, these models offer a potential interaction portal between Standard Model and dark sector particles. 

The 2HDM+a/s also have the capability to explain the 95 GeV anomaly: the CMS and ATLAS groups have reported excesses in the production of tau lepton and photon pairs at the LHC, and an older result from the LEP reports a similar excess in the production of b-quark pairs. These anomalies have all occurred at a similar mass of ~95 GeV, and I investigate the possibility of all three anomalies being caused by a single BSM particle in the 2HDM+a/s. Along with fits to the anomalies and investigation of the dark matter phenomenology of the models, I apply constraints from flavour physics, precision electroweak tests, and collider physics to determine if the 2HDM+a/s remain as viable extensions of the Standard Model.