If an enemy makes it onto your back try flying eratically or press R to elbow the enemy. You could also try boosting but this doesnt always work
To beat him here u must 1st hit him with a disease spell so he loses his shield, then hit him with brisingr or heat breath. If he trys to hit u with lightening fly into the building underneath him for protection. Repeat and u should win. I hope this helps!!!
Once You've finished all the Arena's Missions just go to customize armor and try these patterns out.
FLEET Armor Combo - Helm of Swiftness, Leather Jerkin, Bone Shaffron, Leather Drape, Leather Crupper
GUARDIAN Armor Combo - Chain Coif, Cuirass of Heroes, Chain Shaffron, Faceted Peytral, Chain Crupper
REAVER Armor Combo - Leather Coif, Cuirass of Heroes, Doom Shaffron, Chain Peytral, Leather Crupper
STALKER Armor Combo - Leather Coif, Leather Jerkin, Rock Shaffron, Rock Peytral, Whiptail Crupper
TOTEM Armor Combo - Wood Helm, Wood Breastplate, Doom Shaffron, Faceted Peytral, Bone Crupper