As a DK, I often find myself short of one resource or the other. Either I have too many runes and RP and not enough time, or empty space in my rotation because I screwed up my timing on AMS or am somehow cooldown-less. One ability steps in to save the day: Horn of Winter. If you’ve used Blood Tap, Empower Rune Weapon, and are otherwise empty on runes, Horn of Winter is the only thing left to generate RP. The perks of the spell (even if a Shaman is covering the buff): it’s free and it generates 10 RP. This means that for you Frost DKs playing with the same rotation as me (ITx6 machinegun), you’re going to have a lot of GCDs to fill and sometimes not enough RP. Next time you don’t have ANY runes or RP available to use abilities that do damage, use Horn of Winter.
It took me a little while to get used to turning what was once a once-every-3-minute spell into a use-on-CD ability. It will help you squeeze in extra Frost Strikes and Death Coils, and you’ll never again forget about it and lose the buff if you’re the one providing it to the raid. So just as AMS is used as an offensive cooldown for Frost (purposely activating it and taking spell damage, like walking through fire or other kinds of bad), Horn of Winter can be used in a similar manner. Give it a shot.