The outer halos of galaxies are a fantastic laboratory to study several important physical processes that shape the appearance of galaxies in the universe. While dominated by the dark matter component, the outer halos also harbor small galaxies orbiting around the main galaxy, and often a faint stellar halo. Low surface brightness observations of these stellar halos, as done for example using the Dragonfly telescope, often reveal streams, shells, and several other indicators of merger events, providing a unique insight into the formation pathways of individual galaxies. Additionally, metallicity and stellar population gradients in the smooth parts of the stellar halos provide information about the early formation times of the galaxies. Such global outer stellar halos are commonly observed in galaxy cluster environments, but only recently became available for less massive galaxies. Using the hydrodynamical cosmological simulation set Magneticum Pathfinder, as well as isolated merger simulations, I will demonstrate how to decipher the information hidden in the various components of these outer halos, and what we can learn about the dark components of galaxies from this transition region where the dark component starts to dominate.