As I work on a mod to prevent crashes with Mohora Tanga self-proc overflows, I stumbled across something interesting about Heartbeat Drumming and Swift Flurry. At the mechanical level, these two abilities work in different ways, and the difference matters.

Swift Flurry simply fires a primary attack 33% of the time on crit as you would imagine it works. Every melee weapon crit can trigger it. Very straight forward.

Heartbeat Drumming, on the other hand, works in a different way. When you crit with a melee weapon, 25% of the time it applies a status effect to the target that cannot stack with itself and that status effect then triggers a primary attack from the monk against the target. This extra step is important due to the order in which scripted attacks resolve. In effect, this means that HBD will only trigger once for most weapons that self-proc (such as Mohora Tanga) or for weapons that launch multiple attacks that can proc concurrently (such as Ball and Chain, Sanguine Great Sword, or Sun and Moon), depending on how the attacks these weapons proc are scripted. This is similar to how cleaving stance works under the hood.

This means that HBD is much less useful for chain proc builds than Swift Flurry, not just because the chance to proc is lower, but also because it will always only get one bite at the apple for each set of self-procs or set of eligible attacks that proc concurrently.

To illustrate, a double crit from Sun and Moon should have .747 probability to proc at least one extra SF/HBD attack if they both worked as I assume the community has always thought that they do. However, since HBD can only proc once on the concurrent attacks, that means the actual probability for at least one extra attack is .663. Mohora Tanga is even crazier - with my mod running that cuts off self-procs of Red Flag Flying at 50 in a row, the full chain will only proc one HBD.

Still a meaningful improvement, but less useful, and as you look at the odds to get a respectable chain going, the odds are impacted more and more.

6 minutes ago, ebonfowl said:

To illustrate, a double crit from Sun and Moon should have .747 probability to proc at least one extra SF/HBD attack if they both worked as I assume the community has always thought that they do.

Heartbeat Drumming used to work like Swift Flurry in the early days of the game. As soon as the community found out how easy it was to produce crit chains with both Swift Flurry and Heartbeat Drumming the devs patched it. I never bothered to look into the code, but it was noticeably harder to proc crazy chains afterwards, but still possible.

Your post makes it clear why that is, thank you! 😃

Edited 7 hours ago7 hr by Boeroer