The second boss room from Super Metroid (Metroid 3).
The boss itself was a mindless swinging spiky mouth that could only get hurt by getting shot whenever it opened up. The music was probably the worst part, but it didnt help that the monster only swung faster, kept itself open for shorter amounts of time, and changed color towards red more and more as it got damaged.
Interestingly, its the only boss in the game that is the most easy to face and never lose a single hitpoint the whole time since its one simple scripted event. I still could never battle the monster, i always had my dad take him on. Today its nothing though, ive beaten the game twice on my computer emulator now and the fear is gone.
Ganon from Legend of Zelda: A Link to the Past wasnt very nice either.
As far as one coming to life, out of the TV, id have to say Solid Snake. The second he noticed someone saw him, aka me, he would either snap my neck 50 times or kick me down and shoot me dead in fear of me giving away his positionm. LOL! Or maybe thats just how I PLAY! Well guess whos playing when he comes to life..gahh.