Dustflier

The Dustflier is an Emblem Heartless that is found in Kingdom Hearts 358/2 Days. It can be found at the Station Plaza in Twilight Town after all six of the Heartless bosses fought before it in order to complete the basic requirements of the Mission are defeated. Defeating the Dustflier is the only way to fill the Mission Guage 100%.

Strategy
The Dustflier appears at the Station Plaza after the basic requirements for the mission have been completed. It is vital that the player have Glide or float equipped (preferably glide), and a strong Keyblade. Dustflier's most accurate attack is Fire-elemental, so it would be wise to equip a Ring that defends against Fire damage or Ignite status, such as the Tears of Flame. One gear setup that is helpful is the Ultimate Gear+ (Twilight Blaze+) with 3 ability units, one power unit, and one sight unit. This allows you to deal a fair amount of damage per hit and allows you to get a critical hit more often(critical hits are very effective against the Dustflier).

The best way to defeat Dustflier is to memorize its cues. The Dustflier will move a short distance and then land, creating a powerful shockwave that will cover almost the entire field, as well as the ground itself. Make sure to jump over the shockwave and continue gliding until the field fades from the ground. At this point, the Dustflier will begin an actual attack. The Dustflier will either flip, dash forward, or shoot a bevy of homing fireballs. The first two attacks can be evaded by keeping your distance from the Dustflier, while the fireballs can be avoided by continuing to glide away from them. However, the simplest way to avoid the fireballs is to, as soon as you see Dustflier preparing to launch them, glide behind one of the pillars in front of the Train Station as quickly as possible. If you do so correctly, the fireballs will almost always miss. As soon as you escape these attacks, go for the Dustflier and land at least one combo on it; sometimes you can land up to three. As soon as the Dustflier flies back into the air, glide away from it and repeat this process. If you do get hit by the Dustflier's attacks, you'll lose a great amount of health, and will suffer a status effect. The shockwave, which has no element, inflicts a random status effect, while the Earth-elemental flip will inflict HP-half, the Aero-elemental air dash will inflict Air-Toss, and the Fire-elemental fireballs will inflict Ignite.

Or you could fight the Dustflier only at the top of the steps because its most powerful attack, the shockwave, doesn't register damage here and you are surrounded on three sides by walls. He is kept in place for the most part and can be attacked for much longer and easier.

You could also try a risky tactic with the fireballs: when you see the that Dustflier is firing them air slide quickly to the Dustflier and block all its fireballs, then you're free to land a combo before its next attack. (This won't work without Round Block)

It is a long and difficult battle. Memorize its cues and avoid being hit by attacks, and the mighty Dustflier will go down in time.