The Celestial Assassin 
Introduction
With the release of Fangs of Asterkarn, Ugdenbog Boltthrower received an insane buff that catapulted itself to the premiere leagues. This guide will show off its newly buffed power, and how to get there yourself.
For the purpose of this guide, I will contain several different versions of the same build. There will be a budget, alternative, and minmaxed setup for those seeking differing options.
So why is this build strong? 
The 3 main culprits are Berserkerās pierce damage support (double RR mastery), Onslaught having extremely overtuned damage, and storm spreadās ridiculous weapon damage %.
Pierce builds, outside of niche setups like Belgothian Infiltrators, have often been single RR mastery builds. Examples are the 1.2.1.6 Top 20 build post, where you saw builds such as Pierce Dervishes. Bonechilling Cry + Word of Pain modifiers gives two sources of pierce reduced resistances.
Next is Onslaught. Savagery and Righteous Fervor, along with every other default attack replacer in this game, have modest weapon damage %'s like around 150-160%. Onslaught is 210%. With gigantic flats that gets converted of course.
And finally, Storm Spread. Storm Spread normally fires 8 shots. The weapon we use, Ugdenbog Boltthrower, has a modifier that gives +2 projectiles.
For some added context, all multi shot projectile wps such as Rutnicks, Storm Spread, and Jaxxonās lucky shot multiplies the total numbers of shots by x2. So you have 8 Storm Spread shots, 6 Jaxxon bullets, etc.
Storm spread on its own is 4 bullets. x2 is 8. However, the +2 projectiles mod seems to be added before the x2 calculation. Meaning in this build, each shot of storm spread is 12 shots.
Each hit is 61% weapon damage, for a grand total of 732% weapon damage on a single weapon pool skill.
TLDR - Strongest default attack replacer in the game. Strongest double pierce RR combination mastery. Strongest WPS in the game. Combine all 3? The Celestial Assassin.
Build Overview
Strong levelling AoE with Word of Pain
Absolutely shits out single target damage
Decent survivability (combination of masteries gives good armor, defensive ability, some flat hp, and damage absorption circuit breaker)
Cheap to setup budget version
Beginner Friendly
Faction Choices
MUST side AGAINST Barrowholm. This crossbow will not drop from anywhere except the Barrowholm Cellar.
Kymonās or Vigil, does not matter
Side with Angrim - we will craft for %physique
Devotion Path
+Blue Crossroads
+Sailorās Guide
+Green Crossroads
+Raven
+Kraken
+Yellow Crossroads
+Assassinās Blade - Bind to Onslaught
+Red Crossroads
+Hydra
+Manticore - Bind to Storm Spread
+Mantis
+Toad
- Remove Raven, Green Crossroads, Red Crossroads, Blue Crossroads
+Empty Throne OR Harpy
+Crane
+Unknown Soldier - Bind to Chilling Rounds
+Azrakaa, the Eternal Sands - Bind to Word of Pain
Empty Throne OR Harpy is simple. Harpy is more damage. Empty Throne is more survivability/cc resistance. Your preference
Levelling & Progressing Section
Level 1-10 (click me)
Level 10 Grimtools
Early levels, invest in Word of Pain. This will absolutely steam clean through the early acts. Max out the second node for wide coverage.
The Early Level Package Guideā¢
These are some items that are guaranteed to get via quests or drops that are highly recommended for new players.
[Quest Item] Slith Primal Ring
[Quest Item] Skinner Family Seal
[Quest Item] Sisterās Amulet of Lifegiving
[Monster Infrequent] Brawlerās Distinction
[Quest Item] Fortified Doublet
[Quest Item] Isaacās Spaulders
[Monster Infrequent] Miltonās Casque
These are all itemās that are available in Acts 1 & 2. Highly recommended to learn the routes/quests that offer these items as they give you the necessary start for newer characters.
As I mentioned in my prior guide before, item recommendations (outside of best in slot items) are there as recommendations, often easily to obtain such as faction gear or quest items. If you find a stronger, better equipment piece as youāre progressing that isnāt covered in this guide, use it. There will be many Epic and Legendary item pieces you will find that will be strong. However, for consistency purposes, I will not be covering items reliant on RNG until level 94+.
Level 10-36 (click me)
Level 36 Grimtools
Start investing in some WPS like Storm Spread. Slowly work your way up these trees. We are still relying mostly on Word of Pain to clear.
Once youāre in level range, pickup [Faction Gear] Silvercore Boltās component from Devilās Crossing, and apply it on your weapon. We will be using this component for every weapon upgrade from start of playthrough until finish.
Some recommended items to pickup:
[Crafted Item] Rangerās Helm
[Crafted Item] Gunslingerās Talisman
[Monster Infrequent] Ulrapraxās Sting - This gives +1 to Inquisitor, which is very nice. However, we will replace it in our level 40ās.
[Best in Slot] [Monster Infrequent] Solael-Sect Legguards
[Faction Gear] Devilās Cuirass
[Faction Gear] Devilās Shoulderguard
[Faction Gear] Rhowari Gripās
[Faction Gear] Rhowari Footpads
Ulrapraxās Sting drops here:
Solael-Sect Legguards drop here. It is part of the Hidden Path questline.
Level 36-50 (click me)
The POWERSPIKE ACTā¢
Level 50 Grimtools
When you reach Ugdenbog area, you will want to immediately get these items:
[Best in Slot] [Monster Infrequent] Sylvarriaās Root
[Monster Infrequent] Wendigo Eye - Not BiS, but will cover you from now until endgame
[Best in Slot] [Monster Infrequent] Ugdenbog Boltthrower - Our main weapon
[Best in Slot] [Monster Infrequent] Ugdenbog Waistguard - +1 to Inquisitor belt, amazing value
When youāre in Barrowholm cellar, always open the chest at the end of the dungeon. Its easy to miss. This chest drops all Barrowholm related Monster Infrequents, such as Boltthrower and Wendigo Eye.
At this point, max Storm Spread, Aura of Conviction, and Ranged Expertise. You should notice your damage skyrocketing now.
Some recommended upgrades:
[Faction Gear] Legion Headguard
[Faction Gear] Legion Greaves
Sylvarriaās Root drops here, in one of these 3 potential hidden cave spawn points:
To farm Ugdenbog Waistguard belt efficiently, this boss has a 50% chance to drop. The blue undead crabs are your targets:
Level 50-70 (click me)
You should be finishing up Fangās of Asterkarn / Forgotten Godās, and are now entering start of ultimate at this stage.
Max Vigor for high flat hp for better survivability. Onslaught loses slight value at 11/16 and onwards, so keep Onslaught at 11/16 for now.
At level 70, upgrade all of your previous items that were level 40 to get up to date versions (weapon, amulet, medal, pants).
New Item Upgrades:
[Monster Infrequent] Covenant of Siff - Strong pierce damage ring with stun resistance
[Quest Item] Fortified Doublet (Ultimate)
[Quest Item] Skinner Family Seal (Ultimate)
[Faction Gear] Malmouth Defender Casque
[Faction Gear] Solael Combantant Spaulders
Covenant of Siff drops here, extremely close to Kurn Bonfire Rift:
Level 70-84 (click me)
There arenāt any new item upgrades, as resistances and stats looked good so there was no need for changes. Keep on progressing forward, we are close to the level 94 milestone.
Because this section is the most empty anyways, Iāll use this space to cover Potion Effects. These arenāt really all that useful until much later, whatever you manage to pickup just slap it on as extra bonuses.
Level 84-100 -> Introduction to Budget Build (click me)
Lotās of upgrades here, lets check them out.
[The Goat] Fettan Mask - the classic helmet for all budget builds
[Faction Gear] Elite Bysmiel Nightshroud Chestguard
[Faction Gear] Elite Solael Combatant Spaulders
[Best in Slot] [Crafted Item] Plagueguard Grips - āof Amarastaās Alacrityā suffix is the important one to get.
[Best in Slot] [Crafted Item] Intrepid Warbootās - Coverās strong resistances we lack
Craft in Angrim for %physique bonus, OR craft in Malmouth if you need % stun or freeze resistances.
The most important augments to get, are x3 Hammerfall Powder on your accessories, and a Potent Solaelās Voracity on your weapon. In my playthrough, I wasnāt Revered with Kurn until much later, once weāre Revered with Kurn faction we will swap out weapon augment to Potent Mogdrogenās Bite, as this has incredible OA and DA stats.
From here and onwards, upgrades start getting a bit grindier.
Fettan Mask:
Level 100+ - The Farming Process (click me)
The first item to farm is the relic Aurora.
Fortunately, this is target farmable. In the Glacial Grotto, the mini boss Ulderthorm Tempestborn has a 10% chance to drop the recipe. This should be a fast grind.
The next is to be Nemesis with Cronleyās Gang. The new nemesis, Vinn, dropās shoulders that give +3 to Onslaught and +3 to Chilling Roundās. Perfect for this build! It is recommended to go through Cronleyās lair as much as you can to also stock up on dynamite. We will be needing hundreds of those for later.
The best in slot chest piece, helmet, and medal all are RNG drops. The helmet comes from a recipe. If you do not have another character that can run high SR, Totem Farming on ascendent is the next best thing.
Chest Piece: [Legendary] Mythical Korvoranās Chestguard - Flat pierce damage, good stats, +2 to Deadly Aim & Onslaught
Helmet: [Legendary] Gaze of Fates Unwound - You may wonder why an Aether damage piece is in this build. The biggest star of this show is 8% weapon damage to storm spread. Times 12 shots coming from the weapon, thats 96% weapon damage to stormspread. It also coincidently gives +1 to all skills, and 6% offensive ability. Best possible helmet.
Medal: [Legendary] Mythical Direwolf Crest - 10% weapon damage to Onslaught, +2 to Deadly aim & high flat pierce/OA, but more importantly on every Onslaught attack it converts ALL of your flat cold damage to piercing. Amatokās Pact, Chilling Rounds, Onslaught and any other cold source is now piercing.
The only item that you should care to minmax in particular, is the weapon.
Heart Piercing Ugdenbog Boltthrower of Ruthlessness is the best possible roll. I recommend farming Barrowholm cellar until you get a drop that gives either affixes. Get one that has āHeart Piercingā or āof Ruthlessness,ā you donāt need to aim for both. Once you get a drop with one of them, you can always reroll with Ashes of Awakening to get the other. This is the cheapest route. However, I recommend not rerolling until you get the ascended affixes you want first.
Level 100+ - The Ascended Rerolls & Endgame Minmaxing (click me)
Ascended rerolls will be controversial. Some players would want something cheap, they donāt want to grind in a singleplayer game like Grim Dawn. Others enjoy this process, juicing out a character and melting through content.
If you donāt want any reliance on Ascended Affixes, equip 2 rings that gives -10% pierce resistance. These are the 4 primary options you should aim for:
[Legendary] Bladetwister Signet
[Legendary] Mythical Sigil of the Stone Thane
[Legendary] [Crafted Item] [Faction Gear] Band of the Merciless
[Legendary] [Crafted Item] Mythical Widowās Bite
If you want a very cheap build relative to Ascended Affixes, roll everything just once. Whatever usable stat you get, keep on each item.
If you want to minmax your gear further to the best possible rolls, we start with ringās first.
From the dynamite you farmed earlier, start exploding as many items as you can via the Tinkerer to get scrap. At Angrim, start crafting level 90 magical ringās. Imperial Signet (golden rings) are the best as they give all damage %, but its not a big deal. Your goal is to get ringās that are Cutthroat ring of Landslides. Like we did for our weapon, get a ring that contains EITHER of the two affixes, not both. We will roll for the other affix with Ashes of Awakening later.
Once you have these rings, roll them for Storm Spread ascended affix. Like how our helmet is good, each ascended affix is 5% weapon damage and 5% proc chance on storm spread. Firing 12 shots, thats 60% weapon damage per ring. Roll ascended affix first always, Ashes are much cheaper to grind.
On weapon, 8% max attack speed is the best roll, however 10% storm spread is acceptable too.
Your goal is to now get -3% Total Resistance on Word of Pain modās on Amulet, Belt, and Medal. This makes your pierce rr become incredibly strong. The reason you get this mod on these 3 items, is the value is -3%. On other armor slots, its -1%.
Now on the rest of your gear, get 5% storm spread proc chance. Your total proc chance on storm spread should be 75%. Getting higher would mean more damage, yes, however we need a second WPS such as chilling rounds to proc Living Shadow devotion.
For affix rerolling, aim to get as much pierce damage and cunning as you can. Aim for pants to be āof Vitalityā as we are lacking in HP.
Speaking of HP, something you can do as an alternative is you go back to Elite difficulty, speedrun through the game, and ally with Barrowholm. ONLY do this once ALL of your gear is complete. Farm reputation back to be Revered, and purchase 4% HP augments, which will drastically be better than the flat +150 HP augments. This doesnāt take that long surprisingly, doing all of the above in this section still takes less time than farming for Alkamos rings & Morgoneth set.
For potions, get Amplicorum, with 50% potion efficacy, and Reverrum. This is 20% total damage modifier. Personally, I wouldnāt get the second total damage modifier that drains your HP. Too fragile. I personally use Ventorus and Draculus for the other 2 modifiers.
Endgame Performance
The Celestial Boss Speedrun. Am I doing Clones just to have Rock of Mages? Partially, theyāre still classified as a Celestial boss, albeit very outdated and easy now with all the powercreep. They should really add Sunder mechanic to each clone, this will give somewhat of a challenge back again.
Callagadra is extremely hard for some reason. fumble fumble fumble fumble fumble
Thanks man