I've been trying to find out what this game was for years, I just remembering it scaring the hell out of me.

I would have been about 3 or 4 years old so around 1993/94.
It was on either the Master System or Mega Drive, I'm not too sure.

I was trying to play Alex the Kidd but wasn't smart enough to do that so must have put in a random game.

I only got as far as the start of the game before I legged it outta the room.
Here is what I remember of it.

It started with showing you a fleshy tunnel that led off into the distance and round a bend.
Then a creepy looking head came floating towards the screen at you then the head opened its mouth really wide.
Next what I think was a spaceship either flew from behind it or out of the heads mouth.

At that point I got scared and ran away

I sometimes wonder if it was just a nightmare as I haven't seen anything like it since then.

Ring any bells?