Ruler of the Sky

The Ruler of the Sky (スカイルーラー) is a Heartless Boss exclusive to Kingdom Hearts 358/2 Days. When Captain Hook and Mr. Smee dig up a treasure chest decorated with a dragon skull and buried next to a golden sword, the pirates' darkness awakens the Heartless that lays inside. The Boss then challenges Roxas while the Nobody explores Neverland. Upon its defeat, the Ruler of the Sky plummets into Captain Hook's ship, crushing it. As the Heartless Boss fades away into the light, the heart it held prisoner is finally released. Ruler of the Sky is fought on Day 301.

Kingdom Hearts 358/2 Days
You need to destroy all the tail segments of this avian Heartless to reveal its core. ''After each segment is destroyed, the Ruler of the Sky will glow red and charge its foes. Wait too close to the water's surface and it will fire a salvo of water shots.'' Once the core is exposed, avoid the spray of coins and counter with Fire magic.

Kingdom Hearts 358/2 Days
Right before you battle the Heartless, Pete shows up and explains his plans of his heartless army and threatens that his Heartless will gobble Roxas up for ruining his plans in Agrabah.

Strategy
The important thing to remember when facing the Ruler of the Sky is to not underestimate the Boss's true power. At the start of the battle, immediately Lock-On to the Heartless Boss. You must chase it around while airborne, so attack whenever possible. The best time to strike is as the Ruler is turning. Equipping a leveled-up Glide ability and a good midair weapon will make it easier to keep up and land hits. Be careful if you find yourself behind the Ruler of the Sky, as it will cause pillars of ice to shoot up in its wake, and it will release homing balls of energy from the end of its tail. The energy spheres may drain your HP on impact.

After sustaining about half a bar of damage, a segment of the Ruler's tail will break. At this point, the Ruler of the Sky will enter a berserk state and glow with a pink aura. It will also release a burst of energy as it begins its berserk attack. It will begin swooping back and forth in an attempt to hit you. Occasionally it will release a homing ball of energy when it begins its rush. If you fly too close to the water, it will drop homing energy balls in rapid succession. Try to dodge downwards and to the side to avoid its rush without going too low. If you do go low, use the terrain to your advantage to avoid the energy spheres.

After rushing several times, the Ruler will dive into the ocean. When this occurs, wait for it to resurface, and watch your map. Try to keep out of its range, as the Ruler of the Sky will begine firing coins from its treasure chest-like mouth. Staying low will allow you to avoid this attack. While it's firing, the Boss will move away from you if you try to approach it, so try not to push it outside the area boundary. When it stops firing, it will be stationary for a short time, so start swinging at the tail. Soon the Boss will begin flying like before, so repeat the previous strategy until all tail segments are destroyed.

When the tail has been destroyed, the Ruler of the Sky enters a new berserk state. It will begin flying around the area, circling you with iceberg towers and firing energy sphere after energy sphere. To best avoid its attacks, fly in the opposite direction as the Boss, taking care to avoid the icebergs.

After the berserk state ends, the Ruler of the Sky will stop circling and begin firing coins. This time it will stay stationary if you approach, so come up underneath it and target its core with your weapon and Fire attacks. If you end up above its body, you can still inflict damage to the core. When it's done firing, the Ruler will transform its wings into claws and start swiping at you. Avoid this attack by flying directly away from it. The Ruler pauses for a few seconds after it finishes this attack, giving you an extra opportunity to deal damage. After that it will return to its second berserk state, so repeat the second part of the strategy until the Heartless falls.

As always, equip plenty of healing spells and items, as well as multiple casts of Fire magic. Equipping rings that protect against ice or water will help. Make use of your Limit Break, and equip a weapon with powerful strikes, as the Ruler does not stay still long enough for combo-based weapons to be effective.

A possible strategy to follow is to bring a large number of high-level Fire and Firaga casts, as well as Hi-Ethers and Elixirs to replenish your magic. During the first phase of the battle, use Fire to inflict damage on the tail segments, as its homing capability will make it easier to connect with the target. After the tail is destroyed, use Firaga at close range to inflict a great deal of damage to the Boss's core.

This is one of the longest and most tedious boss battles in Kingdom Hearts 358/2 Days.

Trivia

 * The Ruler of the Sky resembles many things commonly associated with pirates, such as treasure, swords, parrots and skulls.
 * Interestingly enough, if you are hit by the boss's coin shot attack, you will recieve Munny.