I couldn't finish 'em. Looks like this's gonna get complicated.
You trespass upon my domain, tainted of Light!
Leviathan is fought as a boss in Final Fantasy XIV.
The Whorleater (Hard)Edit
Leviathan has two targetable body parts, the head and the tail (both labeled as "Leviathan"), which appear on opposite edges of the Whorleater. Leviathan's head reflects ranged projectiles, while the tail reflects magical damage. Leviathan's health is shared by both ends.
Throughout the fight, he will retreat into the water, performing a dive across the deck of the ship, or body slamming into the deck causing it to tilt. Players will slide towards him during a body slam. Eventually, four Gyre Spumes will appear in four corners of the deck, which must be killed to ensure the Elemental Converter can be used to protect against his Tidal Wave attack.
Unlike the extreme fight, this battle is purely for story progression and contains no treasure box. However, there's a chance a player may obtain a Leviathan Barb, which is used to craft special Leviathan barding for Companion Chocobos.
The Whorleater (Extreme)Edit
In this fight, the off-tank will gain a "Briny Veil" effect that causes any healers to have reduced healing range each time they heal them. It is essential to watch for splashing water every time he takes to the water, as it heralds where he will dive or slam into the barge.
At the start, Leviathan remains at the north end. Once he takes a certain amount of damage, he will retreat into the water and slam into either the north or south end of the Whorleater, sending players sliding in that direction. At this point, the tail appears on the opposite side of his head. After a set time, he will use a Whirlpool attack on both healers in the fight, so try not to crowd near them. Eventually, he uses Tidal Roar to damage everyone before retreating into the water, followed by two lateral dives across the deck, ending with a slam along the north or south end. This sequence repeats itself throughout the fight. The dives occur either along a north-south axis or east-west axis, and the position of his dive will be indicated by a waterspout. Any player that gets hit with a dive will suffer heavy damage and reduced water resistance.
Once his health reaches 85%, two Wavespine Sahagin leap on board and must be eliminated. It is best to ensure they are not on-board while he's diving across the deck. After his first diving sequence, a single Wavetooth Sahagin will emerge. This one is much more dangerous as it can cast spells that inflict Hysteria on party members, including through a persistent black puddle effect on the ground, which is an extreme liability in this fight. It is best to keep it stun-locked.
After his second dive sequence, he will summon four Gyre Spumes. These light brown elementals will siphon energy from the Elemental Converter until they are destroyed. Since each one causes moderate AoE damage upon defeat, it's best to eliminate them one at a time. The Elemental Converter needs to have at least 30% power to properly shield against Tidal Wave, so the spumes must be eradicated quickly with time to spare. He does at least one regular diving sequence during this interval, giving some time to eliminate spumes and let the converter recharge.
Eventually, Leviathan will do a single dive, followed by his signature attack, Tidal Wave. The converter should be activated during or quickly after the dive. As long as the converter has at least 30% power, Tidal Wave won't obliterate the party (with a higher rating further mitigating the damage). However, the railings on the Whorleater are torn off by this attack, which means players can now fall into the sea and will be removed from the fight. This is important as he will soon after use a slam attack (even as the barrier is still up), and anyone not far enough will fall into the abyss.
From here on, the fight repeats like earlier phases, except now he uses Tidal Roar twice and the diving sequences carry the danger of being thrown off the ship. Two more Wavespine Sahagin will appear to harass the party. Once he reaches 40% health, he summons a new set of Gyre Spumes in preparation for another Tidal Wave. By this point, the limit break meter should be at least two bars full (if not three), enabling any Black Mage or Summoner present to use them to eliminate multiple spumes. A common strategy is to just aim it at the two near Leviathan's head, to avoid too much damage from rapidly exploding spumes and to damage Leviathan in the process. As long as the spumes are destroyed quickly, the converter should have enough time to guard against Tidal Wave. However, he has one other trick: as soon as the last Gyre Spume is destroyed, four Wave Spumes appear in the center. Instead of draining the converter, they will tether to whichever player has highest threat rating, dealing damage-over-time before eventually exploding.
Once the second Tidal Wave is used, another Wavetooth Sahagin. It is essential to stun-lock and get rid of it as quickly as possible before Hysteria causes a player to leap overboard. The rest of the fight just consists of evading his usual attacks until Leviathan is slain.
Once the Lord of the Whorl is slain, a treasure box containing two Wave weapons will appear. In rare instances, a "Mirror of the Whorl" or the elusive Enbarr mount may be in the chest. A player may randomly obtain a Barb of the Whorl used for crafting furniture.