Gigas Shadow

The Gigas Shadow is a Pureblood Heartless that is found in Kingdom Hearts Final Mix and Kingdom Hearts 358/2 Days.

Design
A Gigas Shadow has a vaguely humanoid body structure. It has a round, spherical head with circular, glowing yellow eyes. It also has two long, twisted antennae sprouting out of the top of its head. Each of its hands has three clawed fingers, and its feet are large and lack any discernible digits. With the exception of its eyes, this Heartless's body is completely pitch-black. The Gigas Shadow is identical to the basic Shadow and Mega-Shadow, but is much larger than either of its two relatives.

The Gigas Shadow's name refers to its massive size—"gigas" is a Latin word meaning "giant"—and its otherwise identical appearance to a normal Shadow.

In Final Mix, they are simply normal sized Shadows that gradually grow to their limit(due to Sora being shrunk by the potion, they appear bigger.) The fact that they gradually grow is possible that the effects of the shrinking have effected the Heartless in the world and is starting to wear off, or the Shadows feel they have no need to stay in a shrunken state, preferring to chase Sora in a more advantageous situation. But at a cost, they find their ground sinking method useless, as they do not sink through the ground due to being such visible targets to their small prey.

Kingdom Hearts Final Mix
Gigas Shadows only appear after many waves of Shadows have been defeated in the Bizarre Room. Gigas Shadows attack the same way normal shadows do with the exception that they do not become flat and move along floors. They are large and have much more HP than other Heartless in the area. They can quickly surround and swipe at Sora. This can be avoided by moving into a corner on an elevated surface where the only a few Gigas Shadows can attack at once. If a Gigas Shadow manages to strike Sora, it will escape the fight, reducing the odds of winning a rare Synthesis material.

Kingdom Hearts 358/2 Days
Gigas Shadows are relatively easy to defeat. They are only capable of a claw attack, a jump attack, and becoming flat and moving along the floor. The easiest way is to block their attacks. Blocking a claw attack will do nothing but blocking a jump attack will stun them temporarily, giving you time to do a combo. Repeat this enough times and the Heartless will fall easily.