Hello everyone,
Below is something I posted on the playtest forum a while back to try and put together all the information we had on onslaught and its mechanics. I’m reposting it here in the hopes that it provides some measure of answers all in the same place.
Bear in mind that this is both a work in progress… and outdated to some extend since it was written during playtest. I will do my best to remove irrelevant parts and correct mistakes if you would be so kind as to point them out 
Once FoA is released, people are gonna want a good, well-written in depth guide on the mechanics of Onslaught…
But for now, they will have to settle for mine.
What are onslaught stacks ?
Onslaught stacks is a new mechanic introduced in Fange of Asterkarn. The most obvious source of onslaught stacks is the berserker skill that shares its name, but onslaught stacks can also be gained through other skills when using the right gear mod.
Onslaught stacks do something unique that can be leveraged to fundamentally change the gameplay of a lot of skills.
You can build around the skill onslaught as an auto-attack replacer, and couple it with WPS skills, and it will play very decently. (for more information on using onslaught “normally” see the guide on AAR and WPS
It can also act as a nice supplement of damage if used as a “filler” attack for your main skill…
You can benefit from a few stacks at a time from a mod to a skill you already planned on using.
…Or it can be built around to transform some skills into true heavy-hitters.
In this guide, I will try to explain what I think are the best ways to really leverage the power of this skill.
Which skills work with onslaught stacks?
Any active attack that has a cooldown, that is not coded as a debuff or a pet will get its damage increased by 15% per stack.
Mechanically, Onslaught is a true multiplier, just like “total damage multiplied by” mod you can find on some items.
Even if your build doesn’t make use of any such skill, you can at the very least. make use of those stacks by using an action from one of the movement runes
Here’s the full (hopefully) list of Masteries skill that DO benefit from onslaught stacks:
Blade arc (Mutated)
Forcewave
Blitz
Primal strike
Grasping vines
Phantasmal blades
Amarasta’s blade burst
Ring of steel
Shadow strike
Callidor’s tempest
Olexra’s flash freeze (Not sure, needs testing)
Trozan’s sky shard
Devastation
Panneti’s replicating missile (with gear mod)
Blackwater cocktail (Mutated)
Stun jacks
Canister bomb
Grenado
Sigil of consumption
Doom bolt
Dreeg’s evil eye (mutated)
Bone harvest
Ravenous earth
Horn of Gandarr
Rune of Hagarrad (technically a pet, but an exception has been made)
Rune of Kalastor (technically a pet, but an exception has been made)
Vire’s might
Judgment
Aegis of Menhir
Leap
Rip and tear (Werewolf)
Cold snap (Wereraven)
Here are the skills that DON’T work with onslaught stacks:
Summon skills:
Storm totem
Wendigo totem
Mortar trap
Inquisitor seal
Debuffs:
War cry
Storm box of Elgoloth
Flashbang
Blade trap
Siphon soul
Ill omen
Note: for onslaught to trigger, the skill needs to go to cooldown. So if anything prevents that from happening, the stacks will not be spent and the skill will not receive the bonus.
That includes if you have reduced the cooldown to zero through items or mutators (Like frenetic throw), or if you trigger a “% chance of 100% cooldown reduction” like on Ulzuin’s chosen.
what effects work with onslaught stacks ?
All initial damage inflicted, both damage over time and flat damage will get boosted.
fragments and projectiles will also get boosted. Damage added through “retaliation damage added to attack” will also be multiplied.
Skills that “tick” every second when applied to an enemy are generally classified as debuffs and will not get the bonus, but those that inflict damage over an area (like BWC or Grasping vines) will get every tick for their entire duration buffed. Secondary projectiles (Like Panneti’s proliferation) will NOT benefit. Likewise, secondary skill effects (like Vire’s might volcanic stride, Judgment’s heart of wrath, or Shadow strike’s nightfall) will not get the bonus. For more information on secondary skills, fragments and projectiles, see the Secondary skills guide
If you have different sources of onslaught stacks, they will not add together to determine how many total stacks you can have. For example, if you have onslaught (the skill) up to 9 stacks, and a mod that grants you 3 stacks to a different skill, they will be able to pile together up to 3 stacks… then only onslaught will be able to add to your total, up to 9 stacks.
If you have 2 items that both grant onslaught stacks to the same skill, they will add up together… but that total will not add up WITH your maximum stacks on onslaught the skill.
What makes a good onslaught finisher ?
There are a few ways to make good use of onslaught stacks.
- Skills with a very wide area of effect can apply the stack bonus to a lot of targets at once
- Skills with secondary native projectiles (like canister bomb) will inherit the damage bonus, allowing you to hit the same foes multiple times with the same attack.
- In general, skills that are balanced around having a long cooldown, since you will need time to rack up stacks between applications anyway. Any mods on items that trade increase cooldown duration for more damage is excellence here.
- Skills with a ground effect and a long duration are a great way to spread that onslaught bonus as you’re racking up more stacks.
- But by far the best method (I think) is to use it to inflict MASSIVE instances of damage over time (DoT).
DoTs you say ?
A build designed around DoT will have that damage go on for over 20 seconds, plenty of time to manoeuvre, kite, build up stacks, heal, reapply debuffs, and attack again before your previous attack has worn off. To get started with damage over time, consult the DoT guide for dummies
What are the best skills to leverage onslaught’s power ?
The following assume that you are trying to use onslaught stacks to really push the damage (instead of using it as an AAR or just as neat add-ons)
So baring exceptions, this rating will not take skill mods from items that add onslaught stacks, as they are (usually) limited to about 3-4 stacks… Which is nice… but out of the scope of what we’re doing here.
Here’s my tier list of skills that can really take advantage of onslaught. (This is subject to changes as the meta progresses)
S-tier:
Blade arc, Forcewave, Ring of steel, Leap, Rip and tear, Vire’s might, Bone harvest
These skills all have huge %weapon damage (The main carrier of DoT damage), have a decent-to-good AoE, have tons of gear support, and often have a damage type that is supported by the berserker mastery
A-tier:
Blitz, Aegis of Menhir, Shadow strike, Primal strike
Tier A skills lack one of the things mentioned above. They are still absolutely great, but just a tad under the others. Blitz lack DoT support items, Shadow strike has no AoE, and both Primal strike and Aegis have no good damage type that berserker supports. You can make them all work near S-tier level, but they require a bit more work to get there.
B-tier:
Blackwater cocktail, Callidor’s tempest, Ravenous earth, Devastation, Sigil of consumption, Phantasmal blades, Amarasta’s blade burst, Doom Bolt
B-tier is where you’ll find skills that have no %WD but have a long duration that is worth building around. Aramasta’s blade burst is there instead of A-tier because it has no DoT support to speak of, sadly. Phantasmal blade is there instead of C-tier because it has great support and some %Weapon damage, though not enough to apply high DoT like the others above. Doom bolt is there because of its massive damage and direct onslaught support in the form of the Harbinger set.
C-tier
Cold snap, Dreeg’s evil eye, Trozan’s sky shard, Canister bomb, Grenado
Skills in this tier have no duration or %WD, but have very high innate DoT with good support through items, typically in a damage type that is supported by berserker.
D-tier or below
Grasping vines, Horn of Gandarr, Judgment, Panneti’s replicating missile, Stun jacks
Most of those skills have at least one thing going for them (Massive flat or DoT damage, a duration, a very wide AoE, good item support, etc…) but lack several of the things that make them worth building around. Or at least, build around them in a specific way, they should all still work great with onslaught.
I will not be touching Tier C or D, and only briefly go over B tier, as I feel they might have multiple ways to make them work with onslaught, and it’s a bit outside of the scope of this guide.
Some examples of builds designed to take advantage of onslaught
Here are some hastily put-together builds specifically designed to deliver massive DoTs in a single hit. Many have not been tested, and would most likely be horrible to play as-is. They are meant as examples or starting points.
Blade arc bleed thane
Vire’s might bleed Zealot (Can also be done with Umbra’dol, Legacy of Blood and a bit of chaos conversion)
Ring of steel bleed reaver (Nadaan’s reach on switch to show another option) (or use the Korba set)
Leap bleed zealot
These 4 are build almost the same, and have similar playstyle and performance
Primal strike electrocute primalist This could also work in bleed, or even cold with the right conduit, but electrocute is the easiest to build.
Forcewave internal trauma thane Not reinventing the wheel here, just taking a page from @Crab_Turtle_2112’s build and tweaking it to use onslaught.
Bone harvest vitality decay veilwalker
Shadow strike poison reaver Could also be done with the dunefiend set. If you want to do a frostburn version… just use the Zakull set instead, it’s not worth it 
Callidor’s tempest burn evoker
Aegis of Menhir poison zealot Again, not reinventing the wheel here, just adapted my previous build
Blitz frostburn thane Can also be done easily in internal trauma
What kind of results can I expect out of these ?
Previous single-hit DoT builds were able to get about 1 million damage per second DoT going, with a bit of luck and a good crit.
Most of the above can effortlessly go to 1.5 millions or more, with some getting over 3 millions.
Here’s an example made with the blade arc build linked above
Anything else I should know ?
This is a work in progress, so please send me any edit you feel is appropriate, corrections, additional information, builds to link, videos… anything that can help expand this guide.