You can use corn syrup IF it doesn't have anything extra in it, like vanillin. Add about 20% over the dry measure.
Brown sugar is ok in dark, roasty ales. It will give them a slight molasses flavor.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk