WARNING MAJOR SPOILERS AHEAD.
*** Spoiler - click to reveal ***
NOTE: These missions are all part of Carnen's side quests.
You'll first have to meet Carnen in the forrests of Nurnen.
Then head to Gorgoroth. Destroy the ritual and defeat The Balrog. It'll escape to the city of Seregoth.
Travel there and you'll be riding Carnen as a Caragor. Shoot the stalagmites to slow him down, then outside he'll destroy you as you're kncoked off of Carnen. She'll return to you as a Drake.
Shoot Ice breath at the Balrog, until you can hit him with an ice shard. DO NOT fire one as he shoots his whip at the sky. When he gets stunned hold to shove him through the ice. You need to do this four times. Make sure you hit him at least three times with the a shard to get the bonus too.