Stitch

Stitch is a Summon from Kingdom Hearts II. He is made available by finding the Ukelele Charm in a chest in Hollow Bastion after the first visit to Space Paranoids.

Although his true alien form of four arms total, antennae and hair-like spines on his back is shown in the film, only Stitch's Earth form is seen in Kingdom Hearts II. His abilities are comprised of his blasters and ukulele, and his powers as Experiment #626. The way he arrived at Hollow Bastion and whether or not his unnamed world was destroyed is unknown at this time.

Kingdom Hearts II
Lilo and Stitch (2002)

A strange visitor from a distant planet.

Stitch is very strong for his small size and prone to mischief.

He's always ready to help his friend Sora whenever Sora needs him.

Kingdom Hearts II
Stitch is one of two summons during Kingdom Hearts II that makes a difference to the storyline (besides Genie). His first appearance was when Sora, Donald and Goofy went into the corridors leading to Ansem's study; he was seen crawling above them without their notice. During the next cut scene, he dropped down onto the keyboard of the computer. Donald jumped onto the keyboard to grab him, but Stitch jumped off with a laugh. As Donald turned around, he mashes the keys, causing the MCP to be alerted.

Later, in a cutscene showing the Final Fantasy characters fighting Heartless in the The Great Maw, Stitch was seen fighting alongside them, using his blasters from Lilo & Stitch. This may mean that in the Kingdom Hearts series, Stitch may be a resident of Radiant Garden. Otherwise, he could have escaped to his unknown world and not participate in the battle to help Sora, Donald, Goofy and the Final Fantasy characters fight against the Heartless. Another alternative may possibly be that Stitch (like Sora and gang), could have stayed to participate in the War until it was over. This may be more appropriate as Lilo's world from Lilo and Stitch can be seen when you summon Stitch with full effects.

Summon
Stitch can be summoned in a battle using the Ukelele Charm. Stitch is unique as a summon because he does not actually enter the field when summoned; he instead jumps and crawls around the HUD features, occasionally licking the screen. After the summoning scene, Sora tries to follow him, but comically hits the TV screen and returns to gameplay. Stitch stays on the HUD and does most of his actions from there. Stitch is a powerful summon. When MP is used he will usually run over and 'lick' the MP bar, bringing it to full. He will do the same to the HP bar. He can shoot down enemy projectiles, effectively keeping Sora from damage. He will also bring out his ukulele, stunning enemies in midair and causing them to drop HP orbs. He will also randomly turn away from the screen and shoot enemies, simply causing them damage. His Limit attack is Ohana(Hawaiian for 'family'), in which Sora uses the Keyblade as a guitar while Stitch also plays on a ukulele.