The 1.30 update is here: Party Dungeons! Achievements! Arcade! We're in the process of adding new info. NOTE: The Web version is not yet updated. There are a few lingering issues Lava needs to fix before that happens.
In the depths of World 1, past the Encroaching Villa, one can reach and fight the Beast of Blunder Hills, the Fright in the Forest, the 30 foot scourge of Dog Bone, the 'Terror who has not returned his 1997 Blockbuster copy of Mighty Ducks 3', Amarok.
Fireball: Occasionally Amarok will raise his sword and send out fireballs. They are fairly easy to avoid and will be well telegraphed where they will land. He will cast more fireballs at a time on higher difficulties.
Stomp: Occasionally he will stomp, which will do a lot of damage if you stand too close but also shoot out rock spikes. To avoid the rock spikes, run to the pit on the left. If you are on the top platform you do not need to worry about this... however...
Uppercut: If you are on the upper platform, Amarok will occasionally do an uppercut, dealing a large amount of damage. Ranged characters will generally not get hit by this as they are out of range. Warriors are generally better off on the lower platform.
Sword Swing: Amarok swings his sword in a downwards arc. If you are in melee range on the lower platform this will not hit you.
Spike Trap: During some attacks, spikes will come up from the ground in specific locations (marked by holes on the ground). Higher difficulties will have more spikes.
Rocket Fist: Amarok aims his arm at you and after a while, he will shoot his fist at you. Once his fist starts pulsating, he will not move his arm, meaning you have time to get out of its path.
Healing Totem: At about half health, Amarok will sometimes spawn a healing totem, which heals him now and then. If you have enough damage you can just ignore it and keep attacking Amarok. If not, you would do well to destroy the totem. It heals 1250 health in normal and 750K in Chaotic.
Shield Totem: Amarok will occasionally put up a shield totem, which will make the shielded body part take a lot less damage. The shielded part changes based on what platform you're on, so destroy this immediately.
If you have low defense it's recommended that you use food in both food slots, since this means you can make more mistakes without dying. With higher defense, you can just tank most if not all of the hits on normal.
Warriors generally do best on the lower platform, where they only really have to avoid the stomp. In melee range on the lower platform, they will not get hit by the fireballs. Warriors can ignore the sword swing unless they have a royal bayonet, gnarled wand, or wooden bow.
Archers and Mages do well on the upper platform. Generally, they won't get hit by the uppercut and only have to avoid fireballs and the sword swing, which hits the entire platform and a bit farther.