引用自 neversigningoff：

I'm stuck with 2 parts of the campaign. First, I don't know how to use the keypad the get behind the waterfall. The code only pops up sometimes. Secondly, I have no idea how to get the red gem that opens the ooze door. Can anyone help?

The code to the keypad behind the waterfall is found in the first cave during the snow section. A number is written on each side of the cave wall.

To get the red gem, you need to backtrack on map 3 after defeating N. Gin. You will find a button in a house near the start of the map. Return to the house near the bridge and a basement will open.

but where is the keypad?

引用自 DeathWish213：

but where is the keypad?

you have to activate a ! block in the boss room, on the left under the blood waterfall