20. Hallway Regression - Altered States (1980)
While it shares a few similarities with The Fly (more on that later), don't think you can just sit back and just wait for some gory transformations. The dialogue is rich in mind-josteling material and great, pure science fiction philosophies. It's important to pay attention because when the mind bending moment comes at the very end, you should have a vast knowledge at what is at stake. William Hurts character has changed his genetic make up and has tittered on the edge of going the way of the dinosaur. Just when it seems he's run the gauntlet of accessing every dormant form in his DNA, he explodes into a blobby monster and well... alters his state. To his horror, he accidentally affects his wife as a lava/magma monster. Their struggle to embrace in their horrific forms is an allegory for their struggling marriage or any two people trying to come together despite their personal battles. The struggle is amazing to watch despite what the outcome might be.