The Groundshaker is a boss from Kingdom Hearts II.
The Groundshaker was a titanic doppleganger-like Living Bone that roamed the Pride Lands after Simba triumphed over the Scar's Ghosts. The ghosts all merged to form the gigantic Heartless--easily one of the biggest Sora ever fought, comparable only to Darkside. The top of the beast was very much like a lush Savannah. It was the boss of the Pride Lands on the return visit.
Atop the Groundshaker was an unnamed witch doctor Heartless that was something like a Shaman. Similar to the Shaman, the witch doctor formed a relationship with the Groundshaker. When the witch doctor's double-mask rotated, the Groundshaker's head would rotate. One side used volcanic fire attacks, while the other side used eerie electric magic.
It is unknown whether the beast or the witch doctor is the Heartless named Groundshaker. It is entirely possible that they are one in the same, as the witch doctor sometimes merges with the beast. However, it is easy to tell what earlier Heartless inspired the Groundshaker--it has uncanny resemblance in attack style to the Behemoth from Kingdom Hearts.
The reward for defeating the Groundshaker is an upgrade to Sora's Thunder magic.
Trivia
- It is believed that the Groundshaker is the largest Heartless that Sora ever fought (excluding World of Chaos)
- Based on the beta screen shots, many fans believed that the Behemoth would appear in Kingdom Hearts II. Instead, the end result was the Groundshaker.