Mission 64: Eliminate the Emerald Serenade

Mission 26 for Kingdom Hearts 358/2 Days is an optional mission that sends Roxas and Axel to eliminate a special new kind of Heartless.

Regular Mission
Destroy the Emerald Serenade

Mission Walkthrough
Ah, a whole new challenge! Once again, you must defeat a new kind of Heartless, but the sneaky Emerald Serenade comes with a few catches. The good news is that it will never attack you and it runs on a path it will never deviate from. On the downside, it moves fast; it moves just fast enough, actually, that even at its slowest speed you still can't catch it, and it only gets faster the more damage it takes. The trick in Emerald Serenade missions, therefore, is ambush.

The Emerald Serenade will fly in a rough figure-eight around the southern end of the main island, and will be at different elevations throughout. First, clear out any Turquoise Marches near the Serenade's path so your targeting will not misfire. Then, find a spot where it will fly into you and damage it. A great spot is in the tunnel underneath the main island; it comes at you along a straight stretch that makes it nearly impossible to miss with attacks and spells. You also have a lot of help in Axel, whose fire magic and attacks will also chip away at the Serenade. The best attacks are magic, followed up by physical attacks if possible, though you will likely only get a couple of hits in before the Serenade soars past. Blizzard and Aero magic work well, but the most useful is Fire; a successful connect will light the Serenade, causing it to take extra damage as it flies around.

Once you have defeated the Serenade, make sure to grab any chests before you RTC.

Video
Video walkthrough here.