Dragon age origins - stuck in the tower!?

i bought dragon age origins yesterday and spent several hours playing. I'm playing as an elf mage (if that's relevant), and have got to the bit where I've been recruited by Duncan %26amp; Alistair, met the King, explored the battle emcampment, done the Wilds quest, and now Alistair %26amp; I have been sent up the tower to light the beacon or something. We met 2 guards along the way which have now joined the party. We got up the 3 floors, only to get to a room where this big monster (demon?) is waiting for us.



The problem I'm having is that basically, i can't figure out how to kill it.

- firstly, my mana runs out far too quickly for me to be able to send continuous spells at it

- when i do send a spell at it, it doesn't hurt it anywhere near as much as any normal darkspawn

- everyone else gets killed before the beast gets half its life depleted, and then I snuff it as well



There's also a small staircase in that room that leads down, but when i try to make an exit through here, the character just stays stuck on the stairs, as it can't seem to get down to escape.



Is there a bug in the game making me unable to escape? Or am I supposed to kill this thing first? If I'm supposed to kill it, a little help would be appreciated.



I actually did have a bug in a second game i played with a human character, where the side door in the main hall of the castle would not let me get through, untill i restarted the game.Dragon age origins - stuck in the tower!?
You cant escape when you fight the troll: Do the following to beat it.



Make Alastair the tank (Melee/Sheild) (Takes the damage)

You: Heal/Spellcast

Set the archer to damage

Set the other melee guy to damage up close with alastair



Use potions.



Plan B: Try and get the monster to follow you, run around the room in big circles while the others shoot and attack it.