I've been looking around, but I didn't exactly find the answer I was looking for. If this has already been answered somewhere and I didn't see it, feel free to give me the link ;D. Anyway, Death Rune Mastery says:
Whenever you use a Death Strike, there is a 30/60/100% that the Frost and Unholy Runes will become Death Runes when they activate.
My question is which Frost and Unholy Runes? Are they the next ones used? The ones currently recharging? The ones currently charging and the next ones used? If you happen to know, feel free to reply and help me out here .