I've been trying to find this movie for a long time now. I watched it as a kid, so my memories are quite vague.

The most impressive thing I remember was some kind of a humanoid alien in a glass casket, with a stone on its forehead which was blinking to indicate it's alive or waking up. There was some kind of expedition that found it in a cave. I think they entered the cave from above and there were hundreds of snakes covering the floor. Unfortunately I don't recall anything about the plot itself.

I believe the movie should be from '80s, or somewhere around that period.

P.S. I talked to my brother who watched it with me. He was even younger at that time, but managed to recall that the expedition found some kind of substance in the cave that made them evil when they touched it and the same stone appeared on their forehead as well. The final scene of the movie was in an airplane - the pilot turns around and people see he also has been "infected" and has that gem on his face.