The Hollow Tree is a dungeon located in North Saliko, and the second dungeon you will likely encounter. It is the first dungeon that features all of the typical dungeon mechanics, including encounters, enrages, binding and scaling.
The recommended level for the Hollow Tree is 15, however even level 12 adventurers should do fine against early bosses, and will likely have leveled up by the time they get to the final boss. Adventurers above level 18 will be scaled down to that level while inside the dungeon.
Bosses in this dungeon are a considerable step up in difficulty, compared to the Deep Mines. A healer is expected for most of them, and is required for the final boss, Noxxara. Noxxara is the first boss that also has a hard mode, in addition to her regular mode.
The first boss is fairly straight forward. Vilefang is guarding four spider eggs that periodically hatch small spiderlings during the fight. These spiderlings need to be defeated, so they do not attack your healer and slow their casts. You can do this using single-target attacks, but a faster way would be using area spells such as a warrior's swipe, a priest's poison dust, a mage's fire wall, or a hunter's arrow shower.
If you kill an egg, spiders hatch from it when it is destroyed. While it is possible to kill all eggs and prevent more spiders from spawning, the damage required to destroy four eggs and four packs of spiders is better spent on the boss.
Note that Vilefang will enrage if lured away too far from her eggs. If you want to complete the "Full House" trophy, you need to split up into two groups, one staying back at Vilefang, while the other one backtracks through the dungeon.
Cladt Scytheclaw (Optional)
Cladt Scytheclaw is an optional boss, who resides on the branch that is below you when you exit the second floor. This is in essence still the same fight that you do during the "Battle on the Treetops" quest: dodge (or smite) Staggering Roar, and defeat the minions he summons. He will also try to push you off the branch, so make sure to not get too close to its edge.
The key difference to the quest fight is that you do not have Akia (who poisons Cladt during the quest fight) with you. As a result, his health and attack are increased significantly. In addition, the entire fight has a time limit of two minutes and 30 seconds, serving as a damage check for Noxxara. Groups that beat Cladt have, essentially, enough damage to also defeat Noxxara.
Once Cladt is defeated, the wall to the inside of the Hollow Tree breaks, allowing adventurers to reenter the second floor through a hidden tunnel.
Note that while defeating Cladt is optional, he is still required for the "Hollow Tree" trophy.
Noxxara is the final boss of the Hollow Tree, and the first boss that could give new groups a bit of trouble, as it requires each of the roles to play their part: damage dealers need to do decent damage to meet the time limit, healers need to heal and dispel, and tanks need to pick up spiderlings, as well as (in hard mode) position Noxxara appropriate. That said, as long as you deal with Noxxara's spells, and keep attacking her, you should be good to go.
- Poison Patch and Poison Dust: First and foremost, throughout the fight, Noxxara will place patches of poison on the ground. Running through these patches does relatively little damage, however standing in them can quickly deal large amounts of damage to you. Ideally, you want to avoid both patches, however the green patch (which does a large amount of damage at once and leaves you with a debuff that makes you take even more damage if you are hit again) is much more dangerous than the purple one (which deals its damage over a long period of time).
- Web Volley: Every once in a while, Noxxara will web any of her attackers in place. Standing in one of the poison patches while webbed can be dangerous. In addition, being webbed interrupts any spell casts, so keep that in mind. As a healer, using Revitalise to heal over time can be very helpful.
- Poisonous Bite: Finally, Noxxara will stack a poison debuff on her target, which needs to be dispelled (through a priest's "Cure Poison") before it deals too much damage.
At 40% of her health, Noxxara summons a number of small spiders. As with Vilefang, these should be picked up and killed with area spells, so that they do not harass your healer. At 5% her health, Noxxara goes into a frenzy, doubling her damage output. At this point you should just finish her off.
After the time limit of five minutes, Noxxara will go into a hard enrage. Adequately equipped groups should be able to defeat her with well over a minute to spare.
Noxxara's hard mode is activated by leaving the Nutritious Egg intact, for the boss to feed on. Doing so will allow her to use her poison patches more frequently, but most importantly double her health, while leaving the time limit to defeat her the same.
In order to deal enough damage to Noxxara before hitting her hard enrage, you need to utilize the green poison patches, which also deal stacking damage to monsters that stand in it. It is important to keep Noxxara inside these patches as much as possible - the damage loss from a 30x Corrosive Poison stack dropping off the boss (because she was outside the patches for too long) will make beating the time limit very difficult.