Water Core

The Water Core is a Pureblood Heartless that appears in Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage- and Kingdom Hearts III.

Kingdom Hearts III
In the Ravine at the base of Mount Olympus, a group of Water Cores are seen turning a normally calm and shallow river and waterfall into overflowing rapids. After the Water Cores are defeated, the area's water returns to normal.

Design
The Water Core's main body is dark and spherical, with a small blue jagged mouth and pair of beady yellow eyes making up its face. On top of its head are a set of aqua-colored cracks, some of which connect outward from the small blue horn atop its head. From the sides of its body are a pair of bat-like wings with long arms that lead down to a set of claws. The bottom of its body is covered with jagged watery spikes which primarily extend downwards, with one larger spike sticking directly out of the bottom of its body.

Kingdom Hearts III
A Water Core can be electrocuted with Thunder and frozen with Blizzard, but it takes a few shots of either to slay a Water Core. Fire is the most effective choice, as it pierces through and destroys its water shield, as well as preventing the Water Core from taking action for 5 seconds. In higher levels, Water Cores can be defeated with just one or two shots of Firaga.