“Iron kills stars” is one of the classics. Young stars burn hydrogen, because hydrogen is the easiest element to fuse and also produces the biggest bang. So, iron doesn’t kill stars so much as it is a symptom of a star that’s about to be done. Of course there are elements heavier than iron, and they can undergo fusion as well. Long story short: iron doesn’t kill stars, but right before a (large) star dies, it is full of buckets of iron.