"What's the scariest tool in the Silent colina Games?"

Are you mostly asking what is most creepy about the game? I thought this pergunta was what weapon or something to that effect...

Pyramid Head's weapons consist of the deadly and heavy Great Knife, which the player can find and use for the rest of the game, and, later, a spear. 

Probably the Bogeyman's sledgehammer. Imagine what a mess that thing could create. Smashing someone's skull to a bloody pulp... Gives me the shivers just thinking about it. Pyramid Head's headwear is quite disturbing as well.

Another memorable note would be the circular saw you get after killing Curtis in SH: Homecoming.

Lastly... the obscuring mist. Imagine walking through that park in the image below, and something jumping at you from that alley...