Corruption of Earth and Seed - Requires level 45 (level 51 recommended)
Blade of Eternal Darkness
Orange and Purple zones
For orange and purple it is also helpful to have a player who can cure poisons, as the non-elites cast poisons which stack and deal a fair amount of damage if left unchecked. Druids and shamans are the best for this task, although paladins work too. If you have a priest main healing, try to find someone who can get rid of poisons. The mobs cast diseases too, which are annoying but less serious.
Once you get past Celebras (where orange and purple converge) the pulls become noticeably more difficult. The mobs hit harder, have more hitpoints, and have a nasty array of stun, silence, and knockdown effects that ruin casting. Once you get past the roaming hydras, your first pull will be three dinosaurs. These dinos don't hit too hard, but they can silence you for up to 10 sec. Here, having two tanks is very helpful because you must keep these mobs off your casters and healers. A rogue can do the trick, but a warrior, shaman, paladin, druid, or even a hunter's pet would probably be better. Note that silence prevents warriors and bear-formed druids from taunting. Druids and mages make these pulls easier thanks to polymorph and hibernate.
The patrols in this section consist of a few elite rock elementals. When the elites die, they break up into non-elite elementals so it is helpful to have two tanks and some AoE to keep the mobs off the healer and mop up the non-elites quickly.
As you approach princess you will face pulls of two large rock giants. Here, having a second tank (of any kind) is important. These giants hit hard and have a fair amount of hitpoints. Let your main tank focus on one giant and your second tank focus on the other. Focus your DPS on the MT's target first. A rogue really isn't tough enough to tank one of these giants, they hit too hard, and your healer will have to spam heals which might pull aggro. They can be stunned, so if a rogue can keep the giant stunlocked it might work, but then you are losing the rogue's DPS against the MT's target. If you only have one tank, let the tank get a few hits on both giants first before you nuke.
It is definitely better to have two tanks for Princess Theradras herself. She fears and has a knockback which throws whoever has aggro roughly 20-30 yards. Also, she occasionally slams the ground which send out waves dealing about 150 damage (for each wave) and knocking everyone down for several seconds, so you must keep her away from casters or their spells will be interrupted during this AoE knockback. If you have a dwarf priest, put fear wards on your tanks. When she throws back one tank, everyone else stops what they are doing until the second tank establishes aggro. Rogues will not cut it as off-tanks, she hits too hard, and your healer will have to spam heals. If you do only have one available tank, a common strategy is to have them back up into the water towards the walls. When she knocks the MT back, they should be positioned to rebound off the wall and come right back to her.
Against the princess, shadow resistance is helpful for the tanks to prevent the Fear effect. Once again, this is handy but not necessary.