I think multi-tool was the correct guess. I think it may have had a graver on the tip that was knocked off. I wonder if when they were cleaning up the bulb of percussion to make the graver they accidentally took too much leaving the big scar on the obverse side. Here's a very similar piece made of Upper Mercer I found years ago on our farm that is similar made on an overshot flake. The background scale is CM. The bulb of percussion was at the tip.
BTW, that almost looks more like glossy Gray/blue Upper Mercer than Onondaga to me. The Onondaga I'm familiar with on Ohio artifacts is a dull gray/brown mottled material. It could be that our stuff is from further west, dropped here by glacier and not as high quality.