This is a bit of a long shot, but perhaps is it Nausicaa: Valley of the Wind. This was a really big title, released in 1984. There was also a US release called "Warriors of the Wind".
While I don't remember any large mushroom houses, there's a lot of large natural features in the landscape of the world, and the main protagonist does a lot of travelling, so at one stage she may have flown through a similar area.
The tentacle person isn't in this, but some of the creatures do have tentacley things that reach out:
One thousand years have passed since the Seven Days of Fire, an apocalyptic war that destroyed civilization and created the vast Toxic Jungle,[Note 1] a poisonous forest swarming with giant mutant insects. In the kingdom of the Valley of the Wind, a prophecy predicts a saviour "clothed in blue robes, descending onto a golden field, to join bonds with the great earth and guide the people to the pure lands at last". Nausicaä, the princess of the Valley of the Wind, explores the jungle and communicates with its creatures, including the gigantic, armored trilobite-like creatures called Ohm.[Note 2] She hopes to understand the jungle and find a way for it and humans to co-exist.