Easiest way to create vintage grane/corners/angles in Ai

I would simply grab the Pencil Tool and scribble a rough edged corner, then use the Pen Tool to close the hard edges.

I’d do this a few times with varying colors and create several different corners, perhaps 6 or 8 corner variations.

The more detail you add to each of your individual corners the better they will ultimately work.

Then it’s merely a matter of dragging the corners to the Symbols Panel to make them symbols and placing instances where you want the corners. Fill in between corners by again grabbing the Pencil Tool and scribbling fill-in shapes.

_{Made with just 2 corners, would look a lot better with 4 different corners.}

While effects and brushes absolutely work, they often come across as “digital”. By that I mean, they appear too uniform and patterned much of the time which removes any sense of human interaction. By manually creating corners you can reuse which are all different, you’ll retain a great deal of the “human” aspect to any illustration/image.

It’s just my opinion, but this extra effort is what separates great illustrations from just standard images.

I do realize this may not be the “easiest” way. But it is the method I would use.