  A binary mixture of super-paramagnetic colloidal particles is confined
between glass plates such that the large particles become fixed and provide a
two-dimensional disordered matrix for the still mobile small particles, which
form a fluid. By varying fluid and matrix area fractions and tuning the
interactions between the super-paramagnetic particles via an external magnetic
field, different regions of the state diagram are explored. The mobile
particles exhibit delocalized dynamics at small matrix area fractions and
localised motion at high matrix area fractions, and the localization transition
is rounded by the soft interactions [T. O. E. Skinner et al, Phys. Rev. Lett.
{\bf 111}, 128301 (2013)]. Expanding on previous work, we find the dynamics of
the tracers to be strongly heterogeneous and show that molecular dynamics
simulations of an ideal gas confined in a fixed matrix exhibit similar
behavior. The simulations show how these soft interactions make the dynamics
more heterogenous compared to the disordered Lorentz gas and lead to strong
non-Gaussian fluctuations.
