Thorim is one of the watchers boss encounters in Ulduar. The encounter has two phases, in the first, the raid has to split in a gauntlet and an arena team. The arena team must fight waves of adds while the gauntlet team makes its way through some trash and a few mini-bosses to Thorim. Upon reaching the boss, he and the gauntlet group join the arena team, starting the second phase which lasts until Thorim is subdued. Both, fire and nature resistance are useful. When attempting hard mode, a little frost resistance gear is recommended.