Harkion has an infinite amount of HP bars (displayed as "???"), meaning that he cannot be killed at all, no matter how much damage he receives. However he will flee after 5 minutes and 40 seconds into the battle.
Another gimmick that is different from other dungeons is that there is no dungeon rank; instead, a counter showing Battle Points replaces it. The player will gain Battle Points by simply doing damage to Harkion: more damage done to him equal to more Battle Points gained. When the battle ends (by surviving or perishing), the Battle Points that the player accumulated determine which reward he or she is able to receive. Note that Battle Points can be stacked by running Land of Judgment again, yet they will reset themselves to zero the next day.
A player will surely notice that he or she can pass through Harkion's legs like they do not have any collision box, but even so, attacking Harkion from there is not a great tactic as his legs boast of a huge defense that reduce by about 90% of the damage dealt to him. While staying under Harkion might be useful to dodge his attacks, the player will not gain many Battle Points by simply sitting and attacking under Harkion.
Another ability that Harkion has is his evasive movement, where he may perfom a slide every time he is taking damage. Due to this nuisance, players must plan and attack with their Specials and Pets when Harkion cannot silde away (that's when he is performing an attack of his own), otherwise their Special skill could be wasted, especially if the Special is a long multi-hit skill.
Lastly, Harkion has other phases that trigger when a certain amount of time has passed in the fight. A cutscene will warn the player that Harkion is empowering himself and changing to his next phase, paired with an attack that usually delivers plenty of damage and eye-candy. Note that Special skill delays may freeze the game time, and Harkion may no longer perform his phase transitions according to the time counter, but several seconds later, depending of how much delay the player has done with his or her Specials.
Every time Harkion changes phase, his attack will be raised and thus his moves will deal more damage than before.
Harkion has six attacks in the beginning, yet he will acquire another one in his second phase. He will also use special attacks during phase transitions.
- Harkion will attack with three large frontal arm swipes. They have a large hitbox, but only the last hit can induce knockdown. From Harkion's second phase and onwards, he will usually follow this attack with the blue wave attack.
- Harkion will swing twice with his claws, leaving a cross-shaped slice that deals damage over time. The frequency of the damage over time increases with each phase Harkion goes through. Also, this is the only attack where Harkion can still perform his evasive maneuver.
- Harkion will lock-on the position of the player with a reticule before hitting the marked spot with an explosion. Note that after few seconds another explosion may randomly occur at the same spot of the previous explosion.
- Harkion will materialize a wormhole behind him that causes four seconds of confusion as well as damaging the player. After he is done materializing, another wormhole will appear on top of the player's position, and an arm will come down crushing him or her.
- Harkion will generate a blue sphere in his hand, which he crushes to disperse four spheres forward and two behind. The spheres does not deal damage until Harkion slams the ground, launching the spheres up (that will deal rapid hits as they arise) in the air which explode at the climax of their travel distance. Each sphere will reach the same or a different height than the others.
- Harkion will roar and send a huge blue wave in one direction, then he will perform a leap to the left or to the right, throwing the player into the air if he or she did not jump. However, no matter what phase Harkion is in, the damage from the leap will always be 1. Harkion will only perform this attack after his first phase transition. Harkion will usually use this attack after the three large arm swipes.
- Harkion's signature attack (apart from the phase transitions) is composed by him leaping and falling to the right side of the map, where he will perform a loud roar that stuns the player, then proceed to fire a big laser beam from his chest, and finally he finishes by firing eight smaller lasers in a fan formation. After this, Harkion will stay idle for about three seconds in order to recharge himself. He will do this attack only once per phase, usually near the time for the next phase transition.
Harkion is the first boss to feature cutscenes that leave out the game UI (except for few things such as player buffs and ping) in order to show more eye-blasting effects.
First Phase: Harkion files in, a lighting charges him as he lands, and his name appears along with his title "Emissary of Judgment" as he stands up in his full might. This cutscene is not an attack, but is rather a visual presentation of the boss.
Second Phase: Triggers when the timer reaches 1:50. Harkion will power up with his "modules" on the chest and unfurl his wings to soar in the sky and dive from the right to the left. Harkion's size is big enough to cover all the four platform levels, so the player must dodge or attain invincibility frames. Then Harkion will return from the left firing a laser from above that covers all the map again. While the dive does medium damage, the aerial laser will do heavy damage, but it will not kill a player in FATAL status. After this, pillars will erupt in succession from where the laser hit the ground, Harkion will land on the right side of the map and he will be able to use his blue wave attack.
Third Phase: Triggers when the timer reaches 3:20. Harkion will conjure two spheres, merge them, throw the newly formed sphere in the air, and fire a laser to it, causing it to disperse into thousands of smaller shards that quickly fall on the map. Each shard will deal high damage, and few of them will surely lead the player to FATAL status, though they cannot kill. Next, while fighting Harkion in his third phase, pillars similar to those from his second phase transition will appear randomly on the map, dealing moderate damage but without the capacity to kill a player in FATAL.
Fourth Phase: Triggers when the timer reaches 5:00. Harkion will rise up in the air, charge energy and unleash two whirlwinds, one on the right and the other on the left. The whirwinds permanently remain on the battle field while moving sideways and travel at different speeds, dealing heavy damage while launching the player, usually killing them. Furthermore, the energy shards from Harkion's third phase transition now randomly fall in the map, sometimes aimed towards the player's position as well. With the two whirlwinds hanging on the map, energy pillars from beneath, and energy shards from above, it will be hard to continue damaging Harkion without getting hit by such.
End: When the timer reaches 5:40, all attacks will cease, Harkion will drop and punch the ground, probably in frustration as he failed to defeat the player after he brought out all of his moves, and he will fly away. The surviving player will still "fail" the dungeon nonetheless.