I think the skull looks like a totem of a Clan. Like, the Knight could be one of the "Moose People". I just noticed today that the Knight is not riding the unicorn but is standing next to it. There is some old legend that the Unicorns will only let the most noble and pure people mount them, isn´t there? But the Unicorn seems to be accepting and waiting for this Knight..
The girl is either just a looker on or she could be like one of those Medieval princesses that were the reason Knights went to quests for? So the Unicorn and Knight could also both be bowing before the Princess-girl before leaving on their quest?