Living Pod

The Living Pod (リビングポッド) is an Emblem Heartless that is found in Kingdom Hearts 358/2 Days.

Kingdom Hearts 358/2 Days
These mid-sized flying Heartless are able to spontaneously appear behind their targets and possess them.

Though they behave similarly to Hover Ghosts, physical attacks won't stagger them.

Remember, there's no shame in falling back to regroup.

Strategy
These Heartless only appear in one mission at Beast's Castle, in which you have to break jars. They randomly appear when the jars are broken, so it's possible to go most of the mission without seeing one. However, when they do appear, they are deadly. Their possession attack will remove a full bar of life from Roxas, and they have much more AP than normal enemies.

Your best bet is to simply get to the other end of the hall when they appear, which will hopefully keep them from spotting you. You can then go back and try to break the remaining jars with a quick combo. However, if they ever fade out while near you, they are about to possess you, so quit what you're doing and run.

If you absolutely must fight them, use Aero spells to knock them into the air, and then Fire spells to inflict massive damage.