  The second Gaia data release (DR2, spring 2018) included a unique all-sky
catalogue of large-amplitude long-period variables (LPVs) containing Miras and
semi-regular variables. These stars are on the Asymptotic Giant Branch (AGB),
and are characterized by high luminosity, changing surface composition, and
intense mass loss, that make them of paramount importance for stellar,
galactic, and extra-galactic studies.
  An initial investigation of LPVs in the Large Magellanic Cloud (LMC) from the
DR2 catalog of LPVs has revealed the possibility to disentangle O-rich and
C-rich stars using a combination of optical Gaia and infrared 2MASS photometry.
The so-called Gaia-2MASS diagram constructed to achieve this has further been
shown to enable the identification of sub-groups of AGB stars among the O-rich
and C-rich LPVs.
  Here, we extend this initial study of the Gaia-2MASS diagram to the Small
Magellanic Cloud and the Galaxy, and use a variability amplitude proxy to
identify LPVs from the full Gaia DR2 archive. We show that the remarkable
properties found in the LMC also apply to these other stellar systems.
Interesting features, moreover, emerge as a result of the different
metallicities between the three stellar environments, which we highlight in
this exploratory presentation of Gaia's potential to study stellar populations
harboring LPVs.
  Finally, we look ahead to the future, and highlight the power of the
exploitation of Gaia RP spectra for the identification of carbon stars using
solely Gaia data in forthcoming data releases, as revealed in an Image of the
Week published by the Gaia consortium on the European Space Agency's web site.
  These proceedings include three animated images that can be used as outreach
material.
