Considering the quick nature of most battles, the target will likely be downed before the instant kill takes effect, making its usefulness limited in random battles. Any boss fight in which the boss has a Luck rating 40 or above is also out of the question because the boss is immune to the stronger status conditions at this point. However, in the first Golden Sun, most of the bosses don't have luck ratings anywhere near as high as 40, meaning that Curse can be put to great use against the Kraken, Toadonpa, Storm Lizard, and Tempest Lizard to make those battles end in no more than 3 turns.