Jalhalla

Jalhalla is the immense, obese leader of all Poes and ghosts who appears as a boss in The Wind Waker and Four Swords Adventures.

The Wind Waker
Jalhalla resides in the core of the Earth Temple, and is responsible for the death of the Earth Sage, Laruto. He owes his existence to a small group of about twelve normal poes, and a mask that uses their power to form Jalhalla. This beast must be brought down in order to partly restore power to the Master Sword, by placing Medli in her new position as the Earth Sage.

Strategy
The trick to bringing him down is to direct light at Jalhalla with the Mirror Shield, causing him to materialize and fall. Link must then lift the giant off the floor with the Power Bracelets and throw him, causing him to roll into one of the purple columns of spikes on the walls. This will cause his body to split into many Poes for the young hero to dispose of. To make the task easier, Link can use the Hurricane Spin technique (if it's learned already) to quicken the job (only five Poes can be killed at any time, however). Link repeats this process to destroy all the Poes by any means to destroy Jalhalla. The boss's mask then appears, dumbfounded that there are no more Poes to use. When he tries to escape, a beam of light solidifies him and causes him to fall to the ground and shatter. Link is then rewarded with a Heart Container and a more powerful Master Sword.

He is found again in Ganon's Tower later in the game. He must be defeated for a second time (in the same fashion) to break the seal to the door leading to Ganondorf.

Four Swords Adventures
Jalhalla also makes an appearance in Four Swords Adventures during the stage Near the Fields, as the boss of both The Swamp and during the Infiltration of Hyrule Castle.

First Appearance
Jalhalla first appears in The Swamp, bearing the form of a giant floating head reminiscent of the Jalhalla in The Wind Waker. To defeat him, the Links must light a Torch activated by a Floor Switch when Jalhalla is nearby. Doing so will stun him, allowing the Links to slash him with his Sword. Doing so will make part of Jalhalla split off into Ghinis, making Jalhalla reduce in size.

Once Jalhalla is defeated, a strange green figure can be seen fleeing The Swamp.

Second Appearance
Jalhalla is seen once again in the Infiltration of Hyrule Castle, in a full Poe-like body. Upon lighting all the Torches using their Lamp, the Links will get sucked into Jalhalla. The same green figure from The Swamp can be seen inside Jalhalla. Slashing him with the sword will eventually destroy him, allowing the Links to free the White Maiden.

Since both of Jalhalla's forms have virtually nothing in common with each other, other than the small green figure at their heart, it is possible that the green figure is in fact Jalhalla.

Trivia
Jalhalla's name may be a play on Valhalla, a kind of warrior's heaven in Norse mythology. His name also sounds similar to Jahannam, the name of the Islamic equivalent of Hell.