This page is for documenting the different development leftovers, not including removed zones and text.
Inside Giga-lakitu's ObjectData file BossJugem.arc happens to be the decompiled source for the BTP (Binary Texture Pallete) filetype. DemoEndingBossJugem.dtp was exported from Maya 2008 Service Pack 1 on 17/3/2010. It's full source is here:
<TEX_PAT_INFO>
{
	version	3.150
	filename	W:/wii-mottomario/murata_sho/data/BinaryData/BossJugem/DemoEndingBossJugem
	toolname	Maya
	source	'Maya 2008 Service Pack 1 - (DemoEndingBossJugem.mb)'
	date	2010/3/17
	time	0:56:47
	host	EADMURATAS
	suitable_joint	cull_more	47
	numjoints	30
	numframes	370
	playmode	onetime
	numtexpats	1
	compress_mat	on
}
<TEX_PAT>
{
	index	0
	mat_name	MtJugemEye_v
	tex_index	0
	numtextures	3
	tex_name	BossJugemEye.0
	tex_name	BossJugemEye.1
	tex_name	BossJugemEye.2
	size	371
	pattern	0 0 0 0 0 0 0 0 0 0
	pattern	0 0 0 0 0 0 0 0 0 0
	pattern	0 0 0 0 0 0 0 1 1 1
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 2 2 2 2 2 2 2 2 2
	pattern	2 
}
<TEX_IMG>
{
	index	0
	name	BossJugemBody
}
<TEX_IMG>
{
	index	1
	name	BossJugemClown
}
<TEX_IMG>
{
	index	2
	name	BossJugemEye.0
}
<TEX_IMG>
{
	index	3
	name	BossJugemEye.1
}
<TEX_IMG>
{
	index	4
	name	BossJugemEye.2
}
<TEX_IMG>
{
	index	5
	name	BossJugemShell
}
<TEX_IMG>
{
	index	6
	name	FurBossJugemScarf_vBody
}
<TEX_IMG>
{
	index	7
	name	jugem_lens
}
<TEX_ATTR>
{
	index	0
	image	0
}
<TEX_ATTR>
{
	index	1
	image	1
}
<TEX_ATTR>
{
	index	2
	image	2
}
<TEX_ATTR>
{
	index	3
	image	3
}
<TEX_ATTR>
{
	index	4
	image	4
}
<TEX_ATTR>
{
	index	5
	image	5
}
<TEX_ATTR>
{
	index	6
	image	6
}
<TEX_ATTR>
{
	index	7
	image	7
}
<MATERIAL>
{
	index	0
	name	FurBossJugemScarf_v
	texture0	6
	texture1	-1
	texture2	-1
	texture3	-1
	texture4	-1
	texture5	-1
	texture6	-1
	texture7	-1
}
<MATERIAL>
{
	index	1
	name	MtJugemBody_v
	texture0	0
	texture1	-1
	texture2	-1
	texture3	-1
	texture4	-1
	texture5	-1
	texture6	-1
	texture7	-1
}
<MATERIAL>
{
	index	2
	name	MtJugemClown_v
	texture0	1
	texture1	-1
	texture2	-1
	texture3	-1
	texture4	-1
	texture5	-1
	texture6	-1
	texture7	-1
}
<MATERIAL>
{
	index	3
	name	MtJugemEye_v
	texture0	2
	texture1	-1
	texture2	-1
	texture3	-1
	texture4	-1
	texture5	-1
	texture6	-1
	texture7	-1
}
<MATERIAL>
{
	index	4
	name	MtJugemShell_v
	texture0	5
	texture1	-1
	texture2	-1
	texture3	-1
	texture4	-1
	texture5	-1
	texture6	-1
	texture7	-1
}
<MATERIAL>
{
	index	5
	name	jugem_joint:lens_tex_v
	texture0	7
	texture1	-1
	texture2	-1
	texture3	-1
	texture4	-1
	texture5	-1
	texture6	-1
	texture7	-1
}
<JOINT>
{
	index	0
	name	AllRoot
	ndisplays	6
	display	0
	display	1
	display	2
	display	3
	display	4
	display	5
}
<JOINT>
{
	index	1
	name	Root
	ndisplays	0
}
<JOINT>
{
	index	2
	name	Center
	ndisplays	0
}
<JOINT>
{
	index	3
	name	JointRoot
	ndisplays	0
}
<JOINT>
{
	index	4
	name	Head
	ndisplays	0
}
<JOINT>
{
	index	5
	name	CheekL
	ndisplays	0
}
<JOINT>
{
	index	6
	name	CheekR
	ndisplays	0
}
<JOINT>
{
	index	7
	name	Glasses
	ndisplays	0
}
<JOINT>
{
	index	8
	name	Hear
	ndisplays	0
}
<JOINT>
{
	index	9
	name	LowerLip
	ndisplays	0
}
<JOINT>
{
	index	10
	name	UpperLip
	ndisplays	0
}
<JOINT>
{
	index	11
	name	LegL
	ndisplays	0
}
<JOINT>
{
	index	12
	name	KneeL
	ndisplays	0
}
<JOINT>
{
	index	13
	name	FootL
	ndisplays	0
}
<JOINT>
{
	index	14
	name	LegR
	ndisplays	0
}
<JOINT>
{
	index	15
	name	KneeR
	ndisplays	0
}
<JOINT>
{
	index	16
	name	FootR
	ndisplays	0
}
<JOINT>
{
	index	17
	name	Scarf
	ndisplays	0
}
<JOINT>
{
	index	18
	name	Shell
	ndisplays	0
}
<JOINT>
{
	index	19
	name	SholderL
	ndisplays	0
}
<JOINT>
{
	index	20
	name	ArmL
	ndisplays	0
}
<JOINT>
{
	index	21
	name	WristL
	ndisplays	0
}
<JOINT>
{
	index	22
	name	FingerL
	ndisplays	0
}
<JOINT>
{
	index	23
	name	ThumbL
	ndisplays	0
}
<JOINT>
{
	index	24
	name	SholderR
	ndisplays	0
}
<JOINT>
{
	index	25
	name	ArmR
	ndisplays	0
}
<JOINT>
{
	index	26
	name	WristR
	ndisplays	0
}
<JOINT>
{
	index	27
	name	FingerR
	ndisplays	0
}
<JOINT>
{
	index	28
	name	ThumbR
	ndisplays	0
}
<JOINT>
{
	index	29
	name	Tail
	ndisplays	0
}
Super Mario Galaxy 2's /StageData/ folder contains the level map, scenario and many other files for each galaxy. What is interesting however, is that it's got many empty folders inside with unused entries.
Here's the full list of zones:
AncientExcavationTest02Galaxy AndoBonusTest AndoPlanetJumpTest AndoSwimTest AndoYoshi2Test AndoYoshiStage AoyagiTest AoyagiTestMore BarrelGravityConversionPlanetZone BonusAZone BossBussunZone BossParadeGalaxy BussunTestZone Chaos2DAutoAthleticsZone Chaos2DBegomanZone Chaos2DBombAutoZone Chaos2DMoveGravityTestZone Chaos2DTogeZone ChaosManHoleWanwanZone ChaosManHoleZone CoconutsGravityZone CoinInfernoPlanetZone CommonTshapeZone ConfirmObj CosmicBirdRoad CylinderExplainTest DarkRainbowCubeZone DarkRiverBombZone DarkRiverCylinderLiftZone DarkRiverDashZone DarkRiverMoveTwinLiftsZone DarkRiverSanpoZone DarkRiverTamaKoroZone DarkRoadTest02PlanetZone DimensionVrTest01PlanetZone DrillPlanetMazeZone DrillUpDownPlanetZone E3MovAppearFleetZone E3MovBigSmall E3MovCloud2DPlanetZone E3MovCloudGardenGalaxy E3MovCloudSliderPlanetZone E3MovCreekPlanetZone E3MovCutTimberPlanetZone E3MovDashYoshiZone E3MovDigMineBossZone E3MovDigMineInsideZone E3MovDigMineStartZone E3MovDrumCloudPlanetZone E3MovFlowerBeeTutorial00Zone E3MovFlowerGardenPlanetZone E3MovFlowerHighlandGalaxy E3MovFlowerJumpBallZone E3MovFlowerPlantPole00Zone E3MovFlowerSlider00Zone E3MovFlowerWallJumpTutorial00Zone E3MovHipDropMovePlanetZone E3MovLightLabyrinthPlanetZone E3MovMarioFacePlanetZone E3MovMizutamaPlanetZone E3MovMokuValleyEntPlanetDemoZone E3MovMokuValleyEntPlanetZone E3MovNailedUpHanaPlanetZone E3MovOpeningCloudZone E3MovPurpleCoinInfernoPlanetZone E3MovRedBlueEx E3MovSearchWanwan E3MovSkyIslandBarrelPlanetZone E3MovSkyIslandShipPlanetZone E3MovSnowYukkinaZone E3MovSnowZone E3MovStartJourneyZone E3MovTubeSliderTutorialGalaxy E3MovYoshiPlanetZone E3MovYoshiYCaptureZone E3YoshiSpinDriver EarthenPipeRoomA EarthenPipeRoomDZone EasyMoveBlockZone EasyRedBlueBlockZone FingerHeadTestZone FireWoodBoxPlanetOrgZone FLDZAKOPRD FollowerDrillBossImageZone GambleDiceTest01PlanetZone GambleDiceTest02PlanetZone GambleDiceTest03PlanetZone GambleDiceTest04PlanetZone GliderDangerCaveZone GoharaTestA GoroDashOrg01Zone HashimotoTest23Map HashimotoTest27Map HashimotoTest42Map HashimotoTestIZone HayakawaBossTestSimpleStage HayakawaBossTestStage HayakawaHeadingPanelEasyStage HayakawaHeadingPanelHardStage HayakawaHeadingPanelSuperStage HayakawaHeadingPanelUltraStage HayakawaRideTestStage HayakawaTestStage HayashidaSwimTest HayashidaTest HoleSphere2Zone HoleSphereZone HoneyBeeSmallVillageTest01Zone HoneyBeeVillageHomeZone IslandFleetNewGavityZone KarakuriWanwanTest KingTossinTestZone KoopaBossLv1Zone KoopaVs1RoadDossun01Zone KyarKyarOutBreak LargeActionPlanetAZone LargeActionPlanetZone LavaFluffZone LavaRelayPlanetZone LavaSwimPlanetZone LeafBoardCoinPlanetZone MagicBlueStarZone MagicDarkMatterDrillZone MagicDarkMatterGCapZone MagicLeafZone Mario64Battan MarioFacePlanetYokobe MarioFaceShipNewTest03Zone MarioFaceShipNewZone MarioFaceShipTest02Zone MessageCheck MinetaStageObjTest MoguchiRestartZone MotokuraSnowAZone MotokuraTest2DEnemy MotokuraTest2DSwim MotokuraTest2DSwim2 MotokuraTest2DSwimMap MotokuraTest2DSwimTutorial MotokuraTestBalloonYoshi MotokuraTestFly MotokuraTestJrLv2Boss MotokuraTestMapObject MotokuraTestNewCastle MotokuraTestNigero MotokuraTestPlanetShip MotokuraTestSnowObject MotokuraTestSwim MotokuraTropicalPurple MtEnemyPark01PlanetZone MtEnemyPark02PlanetZone MtEnemyPark03PlanetZone MuimuiPlanetZone MurataTest MysteryCandyTest01PlanetZone NigeroLv2Test01PlanetZone NigeroLv2Test02PlanetZone NigeroPlanetZone OmoteuLandManholeLift1014Zone OtaTestGalaxy PeachCastle2DMario1Zone PeachCastle2DTest03Zone PeachCastle2DTicoMeetsTest02Zone PeachCastle3DZone PeachCastleFinalStartZone PeachCastleInsideZone PeachCastleTown3DOrgZone PenginAquariumZone PetoTest PettanWalkPlanetZone QuicksandDarumaSamboZone QuickSandFireTestZone RainbowRoadA RedBlueEx RockBowlingLv1Test1PlanetZone RollingRockBowling RotatePurpleCoin RotateWoodChallengeTest01Zone RotateWoodChallengeTest02Zone SearchWanwanTest01PlanetZone SeesawCylinderTestZone SeesawMoonTest03PlanetZone SeesawMoonTest04PlanetZone SequenceBeforeKoopaZone SequenceNormalEndZone SequenceStar120Zone SmallPlanetBridgeZone SmallRedBlueClimbZone SpinClimbTowerZone SpinGravityChange2Test SpinGravityChangeTest SpinGravityChangeZone StarCreekTshapeZone StorybookDemoTest01Zone StorybookDemoTest02Zone StorybookTestGalaxy StrangeWaterPlanetZone SugawaraTest Sumaki2DTest SumakiEnemyTest SumakiFlowerTest SumakiNPCTest SumakiSphereTest SumakiTest SumakiWaterTest SurvivalGrapyon02Zone SurvivalKaronCubeZone SurvivalPetariZone SurvivalPukupukuZone SurvivalWanwanZone SwitchMoveBlockTest SwitchMoveBlockTest2 TakeuchiNpcTestZone TakeuchiObjTestZone TakeuchiTestGalaxy TakezawaTestA TakezawaTestAGalaxy TanakaTest TimerSwitchingPlatformTest2Zone TogezoTutorialZone TwoSidesMazeZone VSBossMenbosaPlanetZone VsKokoopaShipLv1Zone VsOtaRockTankLv1Zone WanwanSw01PlanetZone WanwanSw02PlanetZone WatanabeTestF WatanabeTestH WatanabeTestL WatanabeTestO WatanabeTestS WatanabeTestT WatanabeTestV WhiteSnowBlockTest01Zone YamaguchiTest01Zone YamaguchiTest02Zone YamaguchiTestItemDrill YokobeRestZoneA YokobeUsefulMapPartsStageA YokotaSurfingPurpleCoinStage YoshidaTestHammerBros YoshidaTestHammerBrosSecond YoshidaTestHammerBrosThird YoshidaTestKoopa YosshiFacePlanetZone
…and here are the empty galaxies:
GemAsteroidGalaxy HomeCenterTest01Galaxy KoopaCastleGalaxy KoopaVs1Galaxy MarioFaceGalaxy RedBlueExTest01Galaxy SurvivalCosmosGalaxy TemplateGalaxy YamaguchiTestGalaxy ZakoParadeGalaxy
Obviously, most of these are test stages or are from the E3 Demo, but there are many that hint at completely removed stages!