Cloud: I couldn't finish 'em. Looks like this's gonna get complicated.
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In the first battle, it is recommended to plainly damage Ultros by means of Relentless Assault and Cerberus paradigms as when he hits at least half of his max HP, he summons Typhon to help him out.
Ultros is for the most part an easy opponent, as his attacks during the first phase are not life threatening. Octopus Ink does low damage and inflicts Slow and Curse. His basic attack hits for low damage and his most powerful attack Frost Breath, is spread across a wide angle, therefore if the party is far from Ultros the attack does small damage, but can hit multiple times if the position allows him to do so. Despite this, it is usually not a significant threat.
Ultros is susceptible to Poison and other debuffs, which if the player is leveled enough for, can easily cripple Ultros's HP down. When he hits half HP, he will summon Typhon through a cutscene, and he will be at full health.
When the second phase starts, Ultros becomes indeed extremely dangerous, not because his powers increase, but because he becomes the biggest annoyance during the battle. This is largely as Ultros is now full bent on supporting Typhon, who is very powerful on his own, and will use buffs like Bravery, Faith, Protect, Shell, Veil and Vigilance. Ultros is virtually immortal at this point, and if he's even close to dying, Typhon will instantly restore him to full HP, meaning Ultros cannot be felled unless Typhon dies first.
This becomes a problem as Typhon will most likely remain buffed for pretty much the whole fight and his attacks are lethal. Ultros will also use his own attacks, which if properly combined with Typhon's merciless offensive, can put the party in a severe situation easily. When Typhon uses Snort, he will be rendered defenseless with multiple debuffs. At this time, Ultros will dedicate himself to removing each debuff and healing Typhon for 10,000 points for each debuff removed.
Therefore the player must focus on Typhon. Since Typhon will be buffed for most of the fight, the player should do the same, and attack, and heal constantly. Eventually, Typhon will fall.
When Typhon is defeated, Ultros attempts to run away, but Serah and Noel combine their attacks to fry Ultros by means of Cinematic Action. Achieving the "Perfect" score from the Cinematic Action, bestows Ultros's summon crystal to the player.
Ultros is a Synergist and like many other Coliseum monsters he has six ATB gauge segments and his level caps at 13. While his stats are impressive, his skillset is not, for he only learns Protect, Shell and Endless Blessings. Therefore the player would need to make a lot of infusions so that Ultros has more abilities at his disposal. Ultros's magic stat can potentially rise above 1,000, making his Feral Link quite powerful.
Ultros's dialogue paraphrases things he said throughout Final Fantasy VI:
"Have I been a mean octopus?" is what he says in the first battle, "Does that make me a bad octopus?"
"Ink and run" is what he says in the second battle with him when he's defeated, "Well, kids, I hate to ink and run... but I AM an octopus!"
"So sorry, so sorry!" is what he says in the third battle with him after he casts status buffs on himself, "I know what you're thinking... "Man, that was cheap!" Sorry, so sorry!"
"Mr. Typhon, come on down" and "He's not so great with words, but his strength'll blow you away!" is what Ultros says in the fourth battle with him when he brings Typhon into the fight.
Additionally, his personal running gags are seen in his introduction: his love for pretty girls, telling horrible jokes, and hatred of "muscle heads".
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Ultros fooling with Noel.
Ultros about to call Typhon.
Ultros and Typhon.
Battle with Ultros.
Frost Breath.
Octopus Ink.
Ultros flailing his tentacles.
