The Grim Reaper is an Emblem Heartless that is found in Kingdom Hearts II. It is one of the bosses at Port Royal. By exploiting the Medallion, the Grim Reaper can become undead and invulnerable to attack.
 Kingdom Hearts II
When Sora, Donald, and Goofy return to Port Royal to search for Organization XIII, they discover that the Aztec treasure has once again been stolen and that Jack Sparrow has become an undead. They head towards Isla de Muerta to investigate, but are confronted by Luxord, who summons the Grim Reaper to attack them. Though they throw it off the Black Pearl and into the sea, Luxord has his Gambler Nobodies steal some of the medallions. This activates the curse on the Grim Reaper and allows it to revive and knock the heroes onto the Interceptor, which Luxord then sinks with cannon-fire. Once Sora and his friends get to land and recover the medallions, they come to the decision that Luxord must have taken the chest of medallions back to town. They follow him there, where they find the chest and an undead Grim Reaper. They manage to defeat the Grim Reaper, removing the curse on Jack, but Luxord takes the monster's heart and escapes through a Corridor of Darkness.
The Grim Reaper is a vaguely humanoid Heartless with an emaciated, legless, dark pink-skinned appearance. Its eyes are yellow and glowing and are surrounded by black rings. Its head somewhat resembles a human skull, and sports a wide crest on its head that resembles a headdress. Two black, angular, curled horns are present on either side of its head. It appears to have a very long neck, and it wears a black and steel blue garment that covers its neck and shoulders. The Heartless emblem is on the front of this garment. Its lower body is covered by a short, black and steel blue skirt with white bandages wrapped around it. The Grim Reaper also wears black gauntlets decorated by jagged, yellow and grey lines. It carries a large, black staff with a wide, steel blue, anchor-like blade on one end and a small, angular, heart-shaped one on the other end. It often holds the weapon with one finger through a hole in the smaller blade, swinging it like a pendulum.
When under the influence of the cursed gold, the Grim Reaper takes on a wilder, rotted appearance, with its ribs more clearly exposed and its clothing tattered. Its skin becomes a light shade of pink and its clothing becomes predominantly periwinkle and tan. The crest on its head gains a heart-shaped hole in it and its pendulum blades become larger. Three small, ghostly skulls the same color as the Grim Reaper's skin fly around it, each sporting glowing yellow eyes and Heartless emblems on their foreheads.
In Kingdom Hearts II Final Mix, the Grim Reaper's skin, skirt, and the garment around its neck all turn white. Its horns, crest, gauntlets, and the cloth around its waist becomes blue. Its pendulum is also recolored in various shades of blue. Its cursed state has a predominantly yellow body with red and black clothing.
In its normal form, the Grim Reaper is quite weak. Its only two attacks are swinging its scythe and teleporting to avoid damage. Under the Aztec curse, however, its power grows. It can absorb the cursed gold to become immune to physical attacks and its own attacks are powered up. It can use the little ghouls around it as bombs. and can turn into a larger ghoul. It can also twirl its scythe around, creating a tornado to suck in the gold.
The Grim Reaper is first fought on the Black Pearl. It is a simple fight. It doesn't attack much and by now you will be at a high level. Use a combo attack, followed by a Drive. It is a good idea to have Donald and Jack Sparrow in your party. Making use of the Draw ability is also recommended (Follow the Wind, Draw Ring, etc.).
The second battle is harder. The Grim Reaper can absorb the cursed Aztec Gold and become invincible. Use the Reaction Commands Hinder and Loot Launch to stop it, and Return to return the treasure to the chest—each command will restore as many coins as you have. To nullify its magic, it is best to use Thunder or Fire, which can set the Grim Reaper ablaze, though this was oddly edited out for Undead Pirates. To keep it still, it is best to use Blizzard and it also requires less MP. Jack's bombs can also ignite the Grim Reaper and can cause it to run wildly, dropping gold wherever it goes.
When all of the gold is returned to the chest the Grim Reaper will be vulnerable. Attack and repeat. Be forewarned, though: the Grim Reaper has a tendency of constantly taking the coins for its own. It also has an attack that it automatically empties the entire chest and transforms into a giant. It stomps around the field before delivering one strike to the ground and reverting to normal size. At this point, it'll be a little longer to nullify its invincibility as you'll need to strip it of all the coins.