Perhaps something like this:
Costs Runic Power.
Adds a powerful Dot to the target for 10 seconds.
6 Second Cooldown.
Can only be applied at or below 35%.
Now it’s something that you want to keep up 100% during execute phases, it costs Runic Power which means you have to play around and be thoughful with it to prevent yourself from being runic starved or not able to refresh the dot.
Obliteration should proc from it to allow frost to keep their rotation going during execute phase, while UH gets to do more damage through Reaping Talent (UH is supposed to be the dot build)