The Flintstones

Invincibility:
Enter MS_STONE_MAKES_WEIRD_JELLY as a password, where "_" indicates a space.

View credits:
Enter HOAGIE_TAKES_COLD_TREES as a password, where "_" indicates a space.

Level skip:
Enter BARNEY_GRABS_BLUE_TREES as a password, where "_" indicates a space.
Pause game play then press X jump to the next level, or press B to jump to the ending.

Level      Password
-----------------------------------
Bedrock 1  BETTY_PICKS_BLUE_RIBS
Jungle 1   BAMBAM_MAKES_SMALL_ROCKS
Volcanic 1 CLIFF_HIDES_HOT_JUICE
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Note: "_" indicates a space.

Hint:Jungle 3:
On Jungle 3 you will get to a section where you climb down a vine and fall on rocks that sink when you stand on them.
The only way to get past them is to jump to them in the following order: right, right, left, right, right, right, left, right, right.

Hint: Jungle 4: Boss battle:
To defeat the saber toothed tiger, wait until some of the coconuts start to shake. Then, hit the ground with your club to make them fall. Make sure that the tiger is under the coconut so it will hit him. It will take five hits before he is defeated.