thinking about how huntress wizard told finn that fern was a worse version of him that he needed to kill to become better. but fern was actually alive and only died once he chose to fight alongside finn and all of their friends.
he died fighting as his true self in the body his curse created. he died a hero. yet he didn't die in self sacrifice. he died before he could do that. he died because of his choice to rid himself of the curse. he died because he chose to be a hero. he began to die the moment he chose to be good.
his greatest hero's sacrifice was to become the tree and give his heroic potential (in the form of a new sword) to a new hero. his greatest sacrifice was the chance to be a hero