Lingering Sentiment (Boss)

The Lingering Sentiment (留まりし思念) is an unlockable secret boss featured in Kingdom Hearts II Final Mix.

Strategy
Basically, all the player would have to do is to dodge the Sentiment's attacks by using Dodge Roll or Guard, specifically for when it swings his Keyblade around or turns into the jet-ski like object. When starting to attack the Lingering Sentiment, the attacks will be an insignificant amount of damage and the only way to stop this effect is to land a combo on it and the damage it takes will be normal. It will mostly use the whip technique after it has been hurt badly a few times, particularly by a powerful finishing move, so use the Quick Run to avoid this after striking him hard twice. If it transforms into the floating guns, just deactivate Lock-On and fly as far away as possible, and turn around stone pillars to make the guns destroy themselves. For the cannon, just deflect the bomb back at it using Guard, and if it isn't possible, just Dodge Roll through it (it will explode without hurting Sora, but be careful with Donald and Goofy). Once it goes into the berserk state, Guard as much as possible and when it strikes the ground, fly for it. Once it gets ready to strike again, cast Reflect as much as possible until it's attack finishes, where the player should strike it with Thundaga to leave the boss vulnerable to a good retaliation.

Make sure to load Sora, Donald and Goofy with Ethers in case the Sentiment casts the spell on Sora which stops him from using Magic. Be extremely careful when it gets ready to trap Sora in the energy-draining triangle. A good indication is when his Keyblade makes a gun-loading noise. Once you hear it, get ready to Dodge Roll at a specific timing rate to prevent the beam from hitting. At the start of the battle, it will shoot three times, but later on, four, so be on the lookout. After the last shot, strike the Lingering Sentiment hard.

At times, the Sentiment will start running towards Sora. If he is too far away, it will jump towards him and maybe land near Sora, giving the player a striking chance. If the boss is running near you, it will either use a basic but powerful Keyblade move that ends in a drill of energy, similar to Sora's Guard Break, or it will throw his Keyblade into the ground and create a vortex of energy that if it hits Sora, it will take away his ability to either attack or use magic. A small lifebar will appear for the Sentiment and the player will have to drain this in order to regain the lost ability. The best magic to use is either Fire or Thunder, but be sure to equip only one of these with Reflect and Cure. If the player can't use magic, be extremely careful, as Sora will not be able to heal himself. To avoid the drill, just stay in the air above the Sentiment and hit it once it puts it away. In the case of the vortex, be sure to observe the boss and either use Dodge Roll or Reflect at the precise moment, and Sora will escape, but do not try to hit the boss, as it will still be invulnerable.

Watch out for lethal combinations, though, such as the boss trapping Sora in the triangle or, going into the berserk state while he can't Attack or use Magic; or it summoning two guns to aid itself while it flies around on the jet-ski. If the player has Once More and Second Chance equipped and Sora gets hit by one of these combinations, just let the boss keep hitting Sora while he's in the air, and the last bit of energy will stay with him. Once it's over, one should heal if they can.

Despite being the weakest, the recommended Keyblade is the Kingdom Key (given Sora is at level 99), because it gives the Damage Control ability. One can use Fenrir or Rumbling Rose if they please, but Fenrir has the disadvantage of Negative Combo and Rumbling Rose has the Finishing Plus, which will make the Sentiment angry quite quickly and force it to use the whip attack when Sora is not ready to guard. Oblivion would be quite useful as well, but as the Kingdom Key is the weakest, it will take the Sentiment most time to get angry. At first, striking it takes little health away, but gradually, the longer the combo, the more health the boss will lose and the more powerful the finishing move will be.

Occasionally, in times of desperation, one can quickly use Limit Form to regenerate health and MP if they are almost out of both and Donald and Goofy are out cold, but be careful to do it in the right place, as the Sentiment may unleash an attack that will hurt Sora immediately after he transforms, or he might be sent into Anti-Form. If possible, go into Final Form at the start of the battle and immediately revert back once Sora has the chance. It wastes Drive bars, but it's a 100% guarantee that Sora won't go into Anti-Form when trying Limit Form. Do not try to use any special Limit Form moves on the Sentiment, as they will do it little damage. Whenever healing, try to be as close to Donald and Goofy as possible so they can use their Ethers on Sora.

Stick to these rules and observe the Sentiment very carefully, and the player should be able to beat it. The Lingering Sentiment is by far the hardest boss in Kingdom Hearts II Final Mix and was arguably one of the hardest bosses in the series, having no real match until Vanitas's Sentiment in Kingdom Hearts Birth by Sleep.