These are some of my ideas for what they can do to make an Ice subclass in Destiny. You would have to do a series of quest on Europa (due to it being almost all ice) to harness the power of the ice! It would be on all! For example a super for the warlock could be you create a blizzard effect around you that blinds enemies and then you get to shoot ice out of your hands that hurts and slows down enemies (Kind of like stormcaller) For the Hunter they can have a super where you throw Ice spears at people and if they hit near you it does an icy effect under you that slows enemies down For the Titan they could do something like fist of havoc but it sends a shock wave in 6 directions that causes ice spikes to come from the ground and kill and slow down enemies!