The Rainforest theme occurs, as the name says, in a forest, where it rains frequently. Here you can find many monsters that look like forest animals.
You are an explorer that can throw stones. Monsters appear very frequently and can take from one to four stone hits to kill. You can also find Mushroom UFOs which aren't very rare.
It rains frequently and over time (meaning if you keep jumping on the same platform, you will still see the rain start and end). You can often get missions about surviving those rainstorms.