Its kind of a shock to have that monster bearing down on you, eh Flyf15 :)
Its probably there to move some oversize load that couldn't be done with a 747. We get them into YWG every few weeks to transport farm machinery like combines and stuff to Russia. Bombardier is also using them like airbus uses the A300 super transporter. They ship finished Dash-8 and CRJ fuselages from Ireland, where they are built by Shorts, to Montreal, Dorval for final assembaly. Don't know what specificaly is in DEN though?