Avalanche Abaasy is the highest level enemy in Xenoblade Chronicles, at level 120, and most likely the hardest enemy in the game. It only spawns on Three Sage Summit on Valak Mountain, at night and only during a blizzard. You know a blizzard is occuring when the lights emanating from the crystals on the mountain disappear. Also, Abaasy doesn’t spawn like other enemies, but will fly down and land when you get close to its spawn point. Besides being really strong, one of the biggest problems with Abaasy is its spike shield. It is an Instant Death spike shield, so unless you have protection against it (Divine Protect or Debuff Resist), then you are going to die a lot. You would definitely want the Debuff Resist, for other reasons.
Ultra Play Bite - Physical-based Art that deals moderate to high damage against a single target.
Ultra Tail Strike - Physical-based Art that deals moderate damage to a frontal arc, and causes Topple.
Demon Purging Fire - Ether-based Art that hits six times for moderate damage overall. It hits around Abaasy and causes both Blaze and Paralysis.
Ultra Air Crush X - Abaasy’s Talent Art. Physical-based Art that hits a single target for pretty much fatal damage; causes Knockback.
Before doing anything else, you will want to lure Abaasy away from the middle of the arena at Three Sage Summit. This is in case the weather changes and causes Final Marcus to spawn, putting you against two superbosses at the same time. Also, as already mentioned, you want a 100% Debuff Resist for this boss, since the Instant Death spike shield will throw a wrench into your plans easily otherwise. Spike Defence doesn’t matter here, so that can be substituted for something else, like maybe Topple Resist to avoid the Ultra Tail Strike’s status.
Abaasy’s battle will start out like normal, with Ultra Play Bite being the strongest move, until it unleashes Demon Purging Fire. While this Art may not seem particularly strong right off the bat, it hits a total of six times and will likely hit everyone. This Art and Abaasy’s Talent Art are probably why bringing Shulk in a good idea, as Monado Armour is great for reducing the damage from the fiery blaze. Also, it is why you want a Debuff Resist gem on everyone instead of a Divine Protect, as Demon Purging Fire will inflict both Blaze and Paralysis, debuffs that will hinder things immensely.
Should you utilize a Topple Locking strategy, know that Abaasy has a halved Topple duration, meaning each Topple Art you connect with will only last 1.5 seconds, instead of the normal 3 seconds. Abaasy’s Talent Art, Ultra Air Crush X, will probably always down the person it will hit, unless you use Shulk’s Monado Shield (at level 10, of course) to negate it. Of course, you can try to mitigate it with Monado Armour, but that’s still a lot of damage, even with that Art maxed. Also of note is that Ultra Air Crush X will have Abaasy move his position, which could mean another enemy gets aggro’ed or its back against the mountain, possibly making it a little more difficult. So, Abaasy has two auras he will put up during the fight, the first of which is a Crazed one at about 70%.
This one, as with some of the others, will grant him Strength Up and Haste, which can be disastrous for your party. Also, as is the case with the other superbosses, both Shulk’s Monado Purge and Melia’s Mind Blast can be used to dispel it, but Abaasy does resist it. The other aura is an awakening one, happening at around 30% HP remaining, granting Abaasy an extra two levels. This one might not be as dangerous as the others, since it doesn’t directly grant him any buffs. If you want, though, you can use one of the two moves mentioned just above to dispel it.