What are the toughest, scariest monsters/bosses in video games?

[Smeags]

Smeags' Adventures through the Great Unknown:

NES:

Fire and Hammers? Sorry Princess, I'm outta here...

SNES:

Oh boy... that's a big Mother Brain. O_O

Genesis:

Surely it can't get worse than this...

It just got worse... run!

PS:

Staaaars!

N64:


I don't even want to know...

B-but I killed him already! How am I supposed to kill him like this?!

GCN:


That's a big Space Pirate...

Run away!

I just can't kill this guy. :(

Wii:


Giant Skull Dragon Thingy that I have to fight with a spinning top... this'll end well...

She's a bad girl.