Arms Warrior Season 2 Tier Set Bonus
Warrior Arms 12.1 Class Set 2pc: Mortal Strike and Execute damage increased by 10% and when you Slam a target, Slam also deals (100% Attack Power) damage to enemies within 8 yds of it. Deals reduced damage beyond 5 targets.
Warrior Arms 12.1 Class Set 4pc: Overpower damage increased by 15%. Mortal Strike and Overpower increase the damage of your next Slam by 10%, stacking up to 3 times.
Arms' new tier set bonus greatly buffs Slam and even encourages casting it more often in multitarget. While the set would be a small step down from the very powerful bonus of Season 1, an innocuous bug is greatly increasing its performance in Mythic+, pushing Arms to be one of the top competitions on the PTR.
Gameplay wise, it's pretty seamless, though the four-piece bonus to Slam could stack higher to better protect against dry streaks during Execute phases. Exceeding the three stack cap without any Heroic Strike proc to spend them on is quite common.
The Good Bugs
Arms is already very strong in Mythic+ on live, though it's actually gotten actually got a weaker set bonus in Season 2, and no notable tuning to increase the damage of its abilities, so what's causing it to jump to the top of Mythic+ performance on the PTR? Bugs.
The biggest thing inflating Arms' damage actually comes from the new tier set bonus, which causes Slam to also hit nearby targets, even when automatically cast via Fervor of Battle. This Concussive Slam is already fairly strong, accounting for an extra 3-6% damage depending on spec and the exact number of targets, but is further inflated due to unintentionally triggering Mortal Wounds.
Concussive Slam crits the skull target, applying Deep Wounds.
This results in every Cleave having a fairly high chance to apply Deep Wounds to all nearby targets, rather than just the one hit by Slam directly. Effectively reverting the Patch 12.0.5 nerf, this adds another +5-9% in increased Deep Wounds damage, which is quite reliable due to the frequency of Cleave, Arms' high crit rate, and manually casting Slam for even more procs to roll the damage higher. In total, this more than doubles the value of the set in multitarget, which is a significant contributor to Arms' performance in Mythic+ dungeons on the PTR.
Colossus gives a lot of extra benefits to bleeds, contributing to the specialization's overperformance.
Some under-the-hood changes have also caused Dreadnaught to be treated as a distinct spell, causing it to trigger things it shouldn't. Because of this, Martial Prowess gains an extra stack every time Overpower is used and Battlelord also gains an extra chance to reset for each target hit, both of which add quite a bit of extra damage in two-target situations that are common in the upcoming Venomous Abyss raid.
Somewhat ironically, this results in using Slam even less, depending on the frequency of Heroic Strike procs.
The Bad Bugs
Not all bugs are beneficial though. Since the start of Midnight, Slayer has been beset by a little known and seldom discussed bug with the way the game handles asynchronous buffs - that is, buffs whose durations "overlap" instead of stacking traditionally. In the case of Slayer, this applies to Executioner, the buff gained through Slayer's Dominance. On the surface, it's pretty straightforward: the buff stacks 3 times and Deadly Focus increases its duration to 18 seconds.
Each Slayer's Strike adds a stack of Executioner, three strikes enable Sudden Death, which reduces the cooldown of Bladestorm by five seconds per stack.
Asynchronous (aka overlapping) buffs are not new in Midnight, though several were added or converted from traditional buffs as part of the expansion's gameplay-without-weakauras update. Unlike a normal buff, which simply stacks up and continually refreshes its duration, asynchronous ones are meant to be dynamic; continually incrementing and decrementing to create an ebb-and-flow that adds more variance to the gameplay. They also curtail the need to carefully watch buff durations and refresh them at the last second, which was a hallmark of Juggernaut in The War Within. Although they can sometimes be difficult to keep track of, since there's no clear to keep track of when a stack will be falling off, they largely succeed in this... or would if not for a hidden design flaw.
When you read "buff durations overlap," you would probably think that each buff stack has its own distinct duration, which count down separate from one another, but the game actually handles these types of buffs very differently: there's only one Executioner buff which has an 18 second duration and the game doesn't keep track of each individual stack whatsoever. Instead, whenever the triggering ability activates, two things happen:
A stack is added to the buff on your bars, refreshing to its maximum duration of 18 seconds.
Behind-the-scenes, an event is scheduled to remove a stack after 18 seconds (or however long the normal duration of that particular buff is).
So far, this sounds right: you get a new buff stack for 18 seconds and you'll lose a buff stack in 18 seconds... except once you reach the maximum stacks of the buff. Executioner stacks three times, which obviously means you can't gain a fourth stack, so what happens when you trigger it again?
You might think this fourth Slayer's Strike should just replace the oldest stack, but one still fades immediately after.
Nothing. You can't gain more than the maximum number of stacks, so it doesn't create a new stack... but a new event is still scheduled to remove a stack in 18 seconds. You still only have three buff stacks, but now have four expiration events, which will eventually result in removing newer stacks early. This is the crux of the issue: the more procs you get, the faster the buffs will start expiring.
In this case, the most recent stack of Executioner falls off in less than 11 seconds, due to extra removal events queued up in the background.
Not only does this lower the average damage of Execute, it also results in less cooldown reduction for Bladestorm. Even if they don't know exactly how the bug works, anyone who has fought L'ura will recognize how disruptive this can be - sometimes you'll get four or five Sudden Death procs between sets of Crystals during the first phase, yet Bladestorm still inexplicably has 30 seconds left on cooldown. This is because stacks are getting munched and fade much quicker than they should - just track the Executioner buff using the cooldown manager and you'll quickly notice how much they fluctuate. Whether in raid or Mythic+ though, the result is a lot less Execute damage and a lot more inconsistent Bladestorm timing than there should be.
Despite averaging a Slayer's Strike every ~8.6 seconds and the buff lasting 18 seconds, the actual stack uptime is incredibly erratic.
This isn't a Warrior-specific issue either. All asynchronous buffs in the game work this way, but the issue only manifests itself when you reach the maximum number of stacks. Most of these buffs have low enough durations and high enough stack caps that the problem simply never occurs. For Warriors, this is why Master of Warfare isn't affected; the apex simply does not proc frequently enough to exceed its 10-stack cap.
Still Strong, but Uncertain
So, where does that leave Arms Warriors? The specialization still performs quite well, with an excellent two-target toolkit for the upcoming raid and strong funnel potential in Mythic+, but it seems unlikely it will stay quite as strong as it is.
Yeah, it's probably not staying there.
The real question is how Blizzard decides to rebalance when any or all of these bugs are fixed, particularly after the majority of PTR testing has already been completed. It's reasonable to assume that Arms will tumble a few spots, but even losing all that extra Deep Wounds damage should still leave Warriors comfortably in the upper tier of Mythic+ damage dealers, similar to where it is now on live.
