The Throwback Galaxy is a galaxy from Super Mario Galaxy 2 which is a redesigned Whomp's Fortress from Super Mario 64. The music is a jazzy arrangement of the original Super Mario 64 main theme, as the original version was also played on Whomp's Fortress. Although the course is generally identical, a few minor changes have been made.
New enemies have been added, such as Paragoombas, Skeeters and a Wiggler. Other enemies seen first in the original game also return, like Piranha Plants, Thwomps, Whomps, and Sliding Stones. Some Bob-omb Buddies also appear in the galaxy, and even make reference to how Mario seems familiar, a reference to his earlier visit to Whomp's Fortress in Super Mario 64 and its remake. A Whomp is found at the top of the area, and defeating it will open an area where the Whomp King is found. A Comet Medal, Rainbow Notes (released from breaking a crate, playing the Super Mario Bros. underground theme) and a bonus planet featuring Piranha Plants can be found in the stage too. Several Cloud Flowers also appear in the galaxy's second mission.
 Whomp Fortress (Starting Planet)
A planet almost identical to Whomp's Fortress in Super Mario 64. However, the floating islands that contained Red Coins and the area where the Star Switch mission is done in Super Mario 64 DS are no longer found. The cannon used to destroy two walls in a mission in the previous games is replaced with a Sling Star. There are a lot of enemies, such as Thwomps, and Piranha Plants in this planet, and at the top, Mario can defeat a Whomp to access a vertical tunnel which will take him to the underside of the planet where the Whomp King is fought.
 Bonus Planet
There is a teleporter near the base of Whomp's Fortress that leads to the Bonus Planet, which is inhabited by multiple Piranha Plants. If Mario is able to defeat them all within the time limit, he will receive three 1-Up Mushrooms.
During the second mission, the player can use a Cloud Flower to get to the Bonus Planet, which is only a short distance away from the main planet. However, the player will have used all three of their clouds at this point, so they won't be able to get back again.
 Return of The Whomp King
The first mission here is very reminiscent of the same mission in Super Mario 64 and its DS remake, with a few minor changes. When Mario gets to the top, he battles a regular Whomp, which, due to the size changes in the species between Super Mario 64 and Super Mario Galaxy 2, appears to be more or less identical to the original Whomp King in size. The biggest difference between the first star in "Chip off Whomp's Block" and the first star of "Throwback Galaxy" is, upon defeating this Whomp, a hole opens up in the center of the platform, which Mario must then drop down to get to the planet's underside, where the player fights the now even bigger and much tougher Whomp King.
His size is much larger than before, due to the fact that normal Whomps are about the size that he was in Super Mario 64. Because of his size, he also can walk around the battlefield much more quickly than before. The area he will slam down on is now highlighted in red. The Whomp King also has some new attacks, which also make him more difficult. For one attack, he does a short hop, which will stun Mario or Luigi if they are on the ground. This shockwave also occurs when he slams down as his primary attack. A second is when he stomps his right foot down, and a group of Whimps appear from the ground. However, these don't make much of a difference to the battle, as the Whomp King will more or less likely destroy the Whimps himself anyway. He is harder to get on top of, as his increased thickness makes the flat surface of his back higher up than it used to be, so Mario will likely have more trouble getting the chance to attack him than before. Instead of being able to Ground Pound anywhere on his back to damage him, the player must hit a small imprint on his back. Additionally, Mario can't "go through" the Whomp King's body, and he can fall off the arena. When defeated, he will recite the same speech as in the original Super Mario 64, as well as then hitting the ground while muttering "Dang it!" under his breath, before exploding and handing over the Power Star.
 Silver Stars in the Whomp Fortress
In this level, Cloud Flowers and five Silver Stars have been added to the main planet. With the help of the Cloud Flower, Mario must collect every Silver Star in the level. Many of the Silver Stars require skillful use of the Cloud Flower to reach, as one floats directly over a Black Hole behind the fortress, while others are located on clouds that only Cloud Mario can reach. At the top of the fortress floats the final Silver Star. When all the Silver Stars are collected, they will form a Power Star.
This mission makes a reference to the DS remake of Super Mario 64, as there are clouds placed in the exact same area as the new DS exclusive grass area that contained a Bullet Bill and many Piranha Plants.
 Whomp Silver Star Speed Run
This is the Throwback Galaxy's Prankster Comet. The stage is the same as Silver Stars in the Whomp Fortress, only there is a two minute time limit. If Mario grabs the five Silver Stars before the time runs out, he is rewarded with the Power Star. The Bonus Planet is not present during this mission.
 Green Star 1
This Green Star has the player redo Return of the Whomp King. Mario/Luigi must make his way to the moving platforms near the beginning of the course, right below the last one.
 Green Star 2
The next Green Star has the player redo Return of the Whomp King, like the first Green Star. It is located on top of the fortress, Mario/Luigi need to get on top of the Whomp and then perform a Backwards Somersault to reach the Star.
 Green Star 3
This Green Star has the player redo Silver Stars in Whomp's Fortress. It is found far out in the skies of the fortress, near the clouds with coins and a Silver Star. Mario/Luigi must use his clouds to jump out from the cloud with the Star to reach it.
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