Shadow Stalker and Dark Thorn

The Shadow Stalker is a boss from Kingdom Hearts II.

Bearing a close resemblance to Darkball Heartless, an enemy from Kingdom Hearts the Shadow Stalker is the third boss of Beast's Castle. Called upon by Xaldin to capture Belle as a last effort to turn Beast into a Heartless, the chandelier-like creature attacks Sora and his friends by possessing the windows, pillars, chandelier and floor of the castle ballroom. Upon being defeated, it transforms into the Dark Thorn. When merged with the floor, it attempts to devour its foes. Sora can avoid this by staying in motion and jumping. When merged with the window, the Shadow Stalker creates a surge of dark power along the floor, which leaves safe spots to stand on. When merged with a pillar, it attacks with a fierce slash attack. To defeat it, deplete the possessed object's HP Gauge and use the reaction command to force the Shadow Stalker out of the object. The Shadow Stalker is believed by some to be a representation of Beast's soul held captive by his curse.

Journal Entry
A Heartless that attacked Belle in Beast's Castle.

It jumped around on the floor, pillars, and chandelier of the ballroom, creating mayhem.

Strategy
The key to fighting the Shadow Stalker is taking advantage of the few moments it is vulnerable. In the very beginning of the fight, you do not have long to attack it, so make your move quickly. After the chandelier attack, you have an excellent opportunity to Release it and then immediately use Beast's Limit. Once it is out of the chandelier it will end up possessing a pillar - if it does so, be on your guard: the possessed pillar (as well as the pillars around it) will attack.After you knock it out of a pillar, you have a few seconds either to use a Limit or use Valor (you must already be in Valor Form, as there is not enough time to change into it and then attack). When the worst happens, you'll get another chance with Mickey. It is advisable to charge his Drive all the way and then fight the Shadow Stalker. The real challenge of this fight depends on how well you dodge the attacks (or how well you parry them, for that matter).

Video
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Shadow Stalker boss battle