Here's our version:
I cut out grass using construction paper and I let him glued it onto the paper.
For our river,I let him paint the paper with water then sprinkled with kool aid juice mixed berries flavor.
For thick oozy mud,He put a glue on the paper using a paintbrush and sprinkled a cajun powder.
For snow storm,we used a salt over a black construction paper.You can do a swirling motion as you apply the glue.
For our forest,we used twigs and construction paper.Since it is a dark forest,he painted it with black paint shown below,but you can always use a black construction paper as an alternative.
We used a piece of newspaper for our gloomy cave and paint the inside with a black paint.
Very quick and simple.