Probably the most common issue I have seen with most Blood DKs is that they do not use blood tap. Most of them use runic corruption, and a few use runic empowerment. I rarely see blood tap used, so in this article I will explain the advantages and disadvantages of each talent to illustrate why blood tap is better.
The Mathematical Breakdown
Let us start with just looking at what each talent offers as a baseline.
*All of these calculations are ‘per rune strike’, or how much you get from this talent on average every time you rune strike. Also they all assume you are not over capping runes/blood charges.
Runic Corruption (RC): 45% chance per rune strike to increase rune regeneration rate by 100% for 3 seconds. Note that this duration is reduced by haste to keep the value the same at all haste levels.
Every proc you get 100% rate * 3 seconds / 10 seconds base to recharge runes = 30% of a rune back, so 30% of a blood, 30% of a frost, and 30% of an unholy rune every proc. Adding that together gives you 90% of a rune back, if you ignore rune type. So you get 45% proc * 0.9 = 40.5% of a rune every time you rune strike.
Runic Empowerment (RE): 45% chance per rune strike to instantly refund a ‘random’ fully depleted rune. I say ‘random’ because if you have both your frost/unholy runes on CD but only one blood rune, it will always give a frost/unholy rune since they are the only fully depleted ones. This is commonly called ‘gaming’ RE.
The math is pretty simple, 45% * 1 = 45% of a rune back every time you rune strike.
Blood Tap (BT): Every rune strike will give you 2 blood charges, and you can spend 5 blood charges (off the GCD/no cooldown) to instantly restore a fully depleted rune as a death rune. You can store up to 12 charges at any time.
The math is also easy here, you get 2/5 or 40% of a rune back every rune strike, and it is always a death rune.
Summary: Every rune strike, RC gives an average of 40.5% of a rune, RE gives 45% of a rune, and BT gives 40% of a rune.
The Value of Control
At first glance, BT is the loser, and RE is the clear winner. So why do I say BT is better 95% of the time then the alternatives?
It is about control. Blood DK is the squishiest tank and heavily reliant on timing. This isn’t usually an issue on weaker hitting content (like 10 man tanking, flex/LFR), but as you do harder hitting bosses, esp on 25 heroic, it becomes painfully obvious. As an example, on Heroic 25, Garrosh does 900-950k damage every swing to a well geared Blood DK. On 25 man heroic Paragons of the Klaxxi, Ka’roz deals about 1.2-1.4 million every auto-attack to a Blood DK later in the fight as his stacks get higher and higher. This means you are constantly in danger of being two shot.
Even great healers cannot save you from that kind of damage. The boss swings every 1.5 seconds, healers cannot heal 900k+ every 1.5 seconds on a tank for the fight. You do avoid some of the attacks, and shield some of the others but the point is I have definitely had many times where I didn’t avoid a single attack for 10 swings in a row, even with around 49% avoidance vs a raid boss, so you can’t rely on avoidance in every case, and any shield will get destroyed every hit in most cases.
How do you survive fights like that? You have to death strike after every landed, un-absorbed auto-attack. If you don’t have death strike, you death pact or healthstone. If you have none of these, pray you avoid the next attack, or proc purgatory, or just die (the most common one). What this means is you always need to have death strikes held in reserve, and you need as many death strikes per minute available as possible if you get long no avoidance streaks.
The Practical Breakdown
Runic Corruption: 40.5% of a rune every rune strike, but only 2/3 of them are usable for death strike, so you get about 26.73% of a death strike rune. In addition, if you need to AoE hard to kill certain adds in time (mines on Blackfuse, P1 Garrosh, Bats on Thok, Ball Lighting on Lei Shen, ect), you only get about 13.36% of a blood rune back every rune strike to use on blood boil. So in terms of getting the correct runes back, RC is the worst of both worlds; it’s bad for getting more death strikes, and it’s bad for times where you need heavy AoE.
In terms of ability to bank death strikes, RC is average. You can have a frost/unholy pair off cooldown while utilizing every proc, so you can play reactively quite well.
Runic Empowerment: 45% of a rune every rune strike, and if you ‘game’ it properly, 100% of them will be death strike runes. You can also game blood runes instead, but that takes a second to ‘swap’ to the proper rune setup for that, and it’s more awkward since you can’t double rune strike with only 1 rune depleted. But still, this gives the highest death strikes per minute (11% over BT).
In terms of banking death strikes, RE is a complete failure. In order to get death strike runes back, you HAVE to have ALL of your frost/unholy runes on cooldown. So by definition, you have to put yourself in a place where you have zero death strikes ready, and are relying on procs to get the runes back to death strike with. This is a horrible idea on many of those fights, and it will force you into using a lot of externals on yourself that aren’t needed with other talents (which can restrict your raid comp a lot), or cause random deaths that you can’t prevent. Obviously you can hold empower rune weapon/dancing rune weapon with T16 4P to help pad out those times, but that is a DPS loss to do so, and not needed with other talents in this tier.
Blood Tap: 40% of a rune every rune strike, with no randomness, and ALWAYS a death rune. So you always get the rune type you need no matter what. AoEing? No problem, use death runes to blood boil. Need to death strike? Use 2 death runes for that. It is the most flexible of all the Level 75 talents.
For banking death strikes, you can always keep about 1.5 death strikes in reserve with this talent. Basically you either have a frost/unholy pair off CD like with RC, OR you have all of them on CD, but have 10 blood charges banked, and can instantly pop off a death strike on demand. Obviously you don’t want to go over 12 charges, but you can alternate these two states pretty easily the entire fight. And you can even have a pair off cooldown, and like 6-8 charges ready, hence 1.5 death strikes. BT gives incredible flexibility in any situation.
Conclusion
I hope after reading all of this you have a better understanding of why blood tap is better in almost every situation then either of the alternatives. Now, the drawback is that blood tap is the hardest one to use properly, so I will be writing a follow-up to this article about how to properly maximize the usage all 3 of the talents.