Emerald Serenade

The Emerald Serenade (エメラルドセレナーデ) is an Emblem Heartless from Kingdom Hearts 358/2 Days. It is a member of a large family of Magic Heartless, whose names reflect their body color and a music-associated word. The Emerald Serenade, although doesn't attack you will summon many other heartless to do so instead. They are mostly green except their bodies are striped in a repeated green and white pattern. As you fight one they move along the same basic path over and over making it difficult to catch. This means following it would be a waste of time. A serenade is a piece of music appropriate to the evening, characteristically played outside the house of a woman, to woo her. It is not to be confused with the Emerald Blues; though they share the same naming color, they are only similar in that they are members of the same family.

Kingdom Hearts 358/2 Days
These large flying Heartless travel along a set path, making ambush a useful tactic.

Their speed grows faster as their HP drops, rendering them increasingly tricky to finish off.

Strategies
The Emerald Serenade always goes along a specific path, so stay somewhere along its path. Bring along about 5 Blizzara and a couple of Fire/Firaga. Also if a partner tags along, change the settings so he won't do anything or else he will ruin the strategy. First you stay somewhere along the Emerald Serenade's path and stay there. Then when it comes close, use blizzara to freeze it. Then use fire/firaga to deal major damage. You can also just attack it with normal attacks while it is frozen. Keep this pattern up until it is defeated.