Ice Breaker is just one of many exotics from the original Destiny that have made their way into Destiny 2, and it returns with a brand-new catalyst that you’ll need to unlock. Unless you run the dungeon within the first 48 hours of its release in Contest mode, the only way to get Ice Breaker is to run the dungeon until it drops, which might take a while. You can complete a few Triumphs to increase your drop chance, but other than that, there’s no way to guarantee when you’ll get it.