Extras are available as in the Console and GBA releases of LEGO Star Wars II. Like it's counterparts, all Extras are bought from the Cantina, and all Extras are available from the start of the game.
Cost: 125,000
Turns every single floor in the game into a Slippery Slidey Mess. Kind've like the Hoth Levels in Episode V, except everywhere.
Cost: 1,000,000
Makes the character completely invulnerable. Extremely useful as the only way you can die is by falling into a pit.
Cost: 500,000 (Disco), 200,000 (Whitebox), 100,000 (Letterbox), 25,000 (Rainy Day), 35,000 (Lights Out), 125,000 (Old Time), 250,000 (Old West), 175,000 (Medieval), 60,000 (Sunglasses), 150,000 (Moustaches)
All of these Extras cause the Visuals of the game to change in some way. Purely cosmetic. Disco Mode causes the game to flash colours as the game plays, also changes all in-game music to a groovy rendition of the Main Title Theme. Whitebox Mode turns every piece of Geometry White. Letterbox Mode changes the Top Screen's presentation from Fullscreen to Widescreen. Rainy Day Mode causes every level in the game to constantly have rain. Fun. Lights Out Mode simply dims the Top Screen's brightness. Old Time Mode gives the game a scratchy film-like filter, while giving every character a Top Hat and Moustache, also changes the music to the Main Title Theme, although slightly changed? I'm not sure. Old West Mode is similar to Old Time, but gives all characters a Cowboy Hat, also changes the music to a country-styled rendition of the Cantina Theme. Medieval Mode gives all female characters a Crown, and all male characters an Armoured Helmet, and it changes the music to something Medieval-ish I guess... Sunglasses gives everyone Sunglasses. Go figure. Mustaches gives everyone Mustaches. Again, go figure.
Cost: 750,000
Another useful Extra. This causes an Arrow to appear above your player characters head, pointing towards the nearest Minikit Canister. This will only lead you to where they are, not show you how to get them.
Cost: 300,000 (Tiny), 350,000 (Ewok), 50,000 (Pink), 400,000 (Droid), 55,000 (Walkie-Talkie)
This set of Extras does something to the NPC's in the game. Tiny Enemies does exactly what you think, makes every single NPC of every sort incredibly small. Ewok Invasion causes all NPC's to turn into harmless Ewok's. Pink specifically targets the Stormtroopers, turning all of their armour from White to Pink. Droid Invasion is identical to Ewok Invasion, but turns everyone into endless copies of C-3PO. Walkie-Talkie Mode gives everyone a Walkie-Talkie as a weapon, including you...
Cost: 7,500 (Sabers), 25,000 (Parts), 60,000 (Hats), 80,000 (Blasters)
All of these Extras simply add parts described to the Character Creator, usable from the Cantina and from in Levels using the Touch Screen.