Mr. Hackensaw is the antagonist of Gregory McLeod's School flash animation as part of the Halloween 2005 special. He is tall, thin, wears a black shirt and pants, have brown hair and vague resembles Gary Oak with sunglasses.
In School, Mr. Hackensaw appeared as an evil substitute teacher for Regal Valley High School.
He appeared briefly in this Halloween special to teach a small class of 5, in which he managed to kill each one.
He is the guardian of the class because the regular teacher, Ms. Sunnyfeld had been involved in an accident. Weather or not she was killed by Mr. Hackensaw remain a mystery. The only lesson he taught was "IR>U".
Mr. Hackensaw has exhibited a few magic abilities, which although not fully explained, are thought to be due to him being a demon. He has dark magic which can stripe victims of their flesh in seconds, the ability to send people into other or his own dimension and the ability to pull weapons out of hammer space. He also can turn his eyes red.