Tactic-wize this is incredibly easy. This is all you've got to know:
#1 Free Thrall when he is encased in an icy thomb so that he can keep the ambushing forces at bay
#2 When Arcurion's minions begin to surround the canyon you have to watch out for falling debris
#3 NUKE and empty all CDs when Arcurion is at 30% health, as he will unleash a devastating Torrent of Frost dealing 20000 frost damage each second to all enemies and reducing their movement speed by -50%.
Arcurion will occationally cast Chains of Frost, which traps all enemies, preventing them from moving. Healers should also look out for his single target spell Hand of Frost that does 50,000 damage.
Good luck! :)
