What were some of the things that maniac had become famous for in the east end

I recall he unties Cobble's Knot.

It is a knot that nobody can untie.

From the text:

"So you see," said Amanda, "if you go up there and untie Cobble's Knot -- which I know you can - you'll get your picture in the paper and you'll be the biggest hero ever around here and nooo-body'll mess with you then."