Watergleam

The Watergleam is one of the Summon Gems and a key item in Kingdom Hearts. Once taken to the Fairy Godmother, Sora can learn the ability to summon Dumbo in battle.

Although it's unknown what Dumbo's World was, it is noted that the Heartless consumed it. As a strong and pure soul, he was transformed into the gem, which eventually landed in Monstro's body. Sora can find the Watergleam in Monstro after obtaining the High Jump ability from Gepetto.