Super Mario Galaxy/Space Junk Galaxy

Space Junk Galaxy is accessible from the Fountain observation dome. You need 9 Stars to enter.

Boss Fight: Kamella
At the start of the fight Kamella uses Fireball and Shell, so chuck a shell at her for the first hit. Note she is behind the ship and the shell can hit the railings so jumping and throwing the shell makes it easier. Next she hovers over the ship and the fireball splits into two, so repeat the strategy. Now Kamella realizes she needs back-up and uses Summon Magikoopas, so take them out then hit Kamella for the star
 * Attacks
 * Fireball: Kamella throws red energy at Mario which eventually turns into a fireball. After you inflict more hits the the red energy splits up into more fireballs.
 * Shell: Kamella throws green energy at Mario which eventually turns into a shell. The shell doesn't actually hurt you but the green energy does. You need to spin near it to catch it when it is moving.
 * Summon Magikoopas: Kamella summons two magikoopas to help her. The easiest way to defeat them is to throw shells at them.
 * Strategy

Star 3: Tarantox's Tangled Web
For the time being, ignore the Hungry Luma you meet on this level.

Boss fight. Jump into a 'sling pod' (a sticky part of the web), pull yourself back using the pointer, and launch yourself at the Tarantox's backside. Tarantox will turn upside down, and you should then launch yourself at the three weak points on its underbelly. Repeat. If you are having trouble getting behind Tarantox, run along with the acid until Tarantox stops. Using a sling pod, shoot yourself into one of the pods on Tarantox's side. This will stun Tarantox, allowing you to get behind it.

Star 4 (Speedy Comet): Pull Star Path Speed Run
Available when a Prankster Comet is in this Galaxy. Do the same as for Star 1, only within a 4 minute time limit. There are more coins to collect on this level than during Star 1. The time limit shouldn't be a problem on this level, but be careful not to die, as there are no mid-level checkpoints.

Star 5 (Purple Comet): Purple Coin Spacewalk
Available when a Purple Comet is in this Galaxy. Collect 100 Purple Coins within a 2 minute time limit. This purple comet mission is one of the easier levels, as the coins are in bunches of 10, making it very easy to get them. Just be careful to not fall on the way back to the start, where the Power Star appears.

Star 6 (Hidden): Yoshi's Unexpected Appearance
Enter Star 3. Proceed through the level as for Star 3. When you meet the Hungry Luma, feed it 50 Star Bits to create a new planet in the shape of Yoshi's head. Defeat all the Goombas on this planet to gain the Star. However, if you lead all the Goombas to you, start jumping on all of them and each consecutive Goomba you hit after the seventh without touching the ground will give you a one up.