S-TIER | BUILD MERCENAIRE FLAMEBLAST OIL GRENADE GEMLING (@Fubgun) | SAISON 5

Build Video

Build Overview

This Flameblast Gemling build is the league starter Fubgun settled on for the 0.5.5 Forbidden Rites event, and it comes down to two buttons. You throw an Oil Grenade, you charge Flameblast up to its 10 stages, you hit one enemy, and the ignite then spreads across the whole map. Once that first ignition is lit, the entire area clears itself with a single button: Flameblast only needs recasting if the spread breaks along the way.

The multiplier that makes the archetype viable comes from the Gemling Legionnaire. On this ascendancy, Flameblast‘s quality grants an extra 40% elemental damage magnitude per stage: at 10 stages, that’s 400% more damage. Pushing quality to 40%, very achievable with a few Gemcutters Prism, pushes the total past 600%. That’s exactly why this skill is only really playable on Gemling, and why the archetype shot up the event tier lists overnight.

The third argument is the gear, and it’s the one that decides how good your league start actually is. The build needs no mana, no cast speed, no flat damage: just life and resistances. No unique items are required, which makes it playable start to finish in solo self-found (SSF, where you can only rely on what you find yourself). Every bit of space that frees up on your gear can therefore go into rarity: Fubgun clears 200% within the first few days, a level very few builds reach that early.

Strengths / Weaknesses

Skill Gem Setup by Step

This build offers 5 progression steps from leveling through to the final build. Select a step to see the matching gem setup.

lvl 1-14 lvl 15-32 lvl 33-51 lvl 52 Transition lvl 53-70

lvl 1-14

7 skills • 14 gemmes

Tir à l'arbalèteCrossbow Shot

Grenade explosiveExplosive Grenade

Grenade assourdissanteFlash Grenade

Grenade suffocanteGas Grenade

Bombe de givreFrost Bomb

Héraut de la cendreHerald of Ash

BondissementPounce

lvl 15-32

7 skills • 18 gemmes

Grenade explosiveExplosive Grenade

Grenade assourdissanteFlash Grenade

Grenade suffocanteGas Grenade

Bombe de givreFrost Bomb

Héraut de la cendreHerald of Ash

BondissementPounce

Grenade à huileOil Grenade

lvl 33-51

6 skills • 16 gemmes

Grenade explosiveExplosive Grenade

Grenade assourdissanteFlash Grenade

Grenade suffocanteGas Grenade

Héraut de la cendreHerald of Ash

BondissementPounce

Grenade à huileOil Grenade

lvl 52 Transition

6 skills • 23 gemmes

ConflagrationFlameblast

Grenade à huileOil Grenade

Bombe de givreFrost Bomb

Sensibilité aux élémentsElemental Weakness

TornadeTornado

Déclenchement lors de l'EsquiveCast on Dodge

lvl 53-70

6 skills • 29 gemmes

ConflagrationFlameblast

Grenade à huileOil Grenade

Bombe de givreFrost Bomb

Sensibilité aux élémentsElemental Weakness

TornadeTornado

Déclenchement lors de l'EsquiveCast on Dodge

Recommended Equipment

The rule is simple: the spell weapon carries the damage, the crossbow carries the clear, and everything else carries life, resistances, and rarity. Nothing else matters on a Flameblast Gemling Legionnaire build.

• Spell weapon (weapon set 1): a staff with +3 or +4 to fire skills, with increased spell damage or fire damage. It’s the single most important piece of the build. From level 36 onward, +4 to fire spells can show up at vendors, so check them every time you return to town. A sceptre works too, but then you also need to find a decent shield.
• Crossbow (weapon set 2): it contributes nothing to damage at all. It’s only there to enlarge the Oil Grenade‘s area, through gem levels. What to look for: an extra grenade cooldown use (an Abyssal modifier to reveal), skill levels, attack speed as a suffix, on a base that already grants +1 grenade.
• Body armour, helmet, gloves, boots, belt: life and resistances, then rarity wherever there’s room left. A body armour offering skill quality gains a bit more dodge roll distance.
• Rings: rarity and resistances, and above all, no flat fire damage whatsoever, which would break the ignite.
• Amulet: a rare piece with life and resistances is enough for the entire campaign. From the skill swap onward, Fubgun’s setup switches to Surefooted Sigil, which grants an extra meter of dodge roll distance and evasion after each roll. The choice makes sense in light of the next section: on this build, dodge roll distance is both movement and survival comfort.
• Jewels: a Greater Jewellers Orb for Flameblast (one is guaranteed in the Nakanu zone of Act 4), a Lesser for Oil Grenade. A second Greater on the grenade further enlarges the area.

Gameplay Tips

• The mapping rotation: Oil Grenade, dodge roll, Oil Grenade, dodge roll. Flameblast is only worth recasting if the ignite hasn’t spread: no need to reload 10 stages between packs.
• On bosses: Frost Bomb and Elemental Weakness before the burst, plus Tornado. With a decent staff, these three skills become almost unnecessary, because the damage climbs so high.
• Check your character sheet after every gear change: the crossbow’s damage line must only contain physical, cold, or lightning damage. A single point of fire and the ignite collapses.
• Projectile Acceleration I is mandatory in the six-link. Without projectile speed, the grenade lands too close and the area it covers becomes poor.
• Keep all your Gemcutters Prism during the campaign. They’re only useful from level 52 onward, and the gap between two and four represents double the damage.
• There’s no rush to swap skills. Without a good staff or quality, it’s better to finish the campaign on grenades and make the swap later.

Cast on Dodge: the trick that makes this Flameblast Gemling build fast

This is the piece Fubgun presents as his own discovery, and the one that convinced him to play the archetype this season: nobody had paired Cast on Dodge with this setup before. The idea is an elegant repurposing of the ascendancy bonus. On Gemling, Cast on Dodge taps into gem quality, and that quality grants 1.2 extra metres of dodge roll distance.

Direct consequence: quality, which you stack anyway for Flameblast damage, also turns into movement speed. The same investment pays off twice. In practice, this plays out as a very tight loop (grenade, dodge roll, grenade, dodge roll) covering more than half a screen per roll, and even more with a chest piece offering skill quality and the Paragon anoint.

The comparison is worth making, because it explains where this build ranks. Most builds that climb very high by the end of the season start out slow: they rely on attack speed they don’t have yet, or on a chain of movement skills still waiting to be unlocked. Here, the speed is there from level 60 onward, with no extra investment. Fubgun isn’t claiming this is the fastest build of the season: the bow and Tornado archetypes eventually pull ahead, but over the first two or three days, it plays in the same league as they do.

How to scale damage and area of effect

Two distinct mechanics, two separate stat pools: mixing them up is the most common mistake on this Gemling Flameblast build.

For clear speed, you need projectile speed and area of effect. Projectile speed determines how far your Oil Grenade travels: without Projectile Acceleration I, coverage stays poor; with it, it reaches almost the whole screen. Area, on the other hand, scales with your grenade gem’s level, and two conditional bonuses stack on top of it without ever showing on the tooltip: up to 40% area per recently ignited enemy, and 15% more after a recent kill. While mapping, both conditions are met constantly: 55% extra area that appears nowhere on the sheet.

For damage, only spell statistics matter. Skill levels come first, followed by ailment magnitude and damage-over-time speed. Increased fire and spell damage also work, but pay off noticeably less. Crossbow statistics, meanwhile, don’t factor into the equation at all.

The ideal crossbow, and why it deals none of your damage

Counter-intuitive point: your crossbow contributes zero damage. Oil Grenade only carries the ignite lit by Flameblast, it doesn’t create it. So the only stat that actually matters on this weapon is how many levels it grants to the grenade, because the skill’s base radius grows with its level.

Three breakpoints shape the choice. A level 19 gem with a +3 crossbow reaches 22, for a base radius of 2.7. A level 20 gem with a +5 crossbow reaches 25 and a radius of 2.8. At 28, it moves up to 2.9. These weapons are cheap because only one stat matters: unless you’re unlucky, you’ll find yours without spending any currency on it.

Fubgun’s end-game crossbow combines three lines: an extra grenade cooldown use (an Abyssal modifier still to be revealed), maximum skill levels, and attack speed as a suffix. An essence guarantees the attack speed, Abyssal currency handles the rest. It’s a weapon you can put together from day one, and its only job is to make the grenade fly farther and more often.

Switching to Flameblast at level 52: the full checklist

The campaign is cleared entirely with grenades, from level 1 to level 51, because Flameblast is a level 52 gem. That’s not a stopgap: Explosive Grenade with Short Fuse I, then Flash Grenade with Grenadier, crush packs and drop bosses almost instantly. Act 1 stays a bit sluggish; Act 2 changes everything.

On the weapon-upgrade side, the path is clearly marked: a Tense crossbow at the Red Vale, a Sturdy one at level 10, important before Count Geonor, then a Varnished one at level 16, which deserves serious investment (regal or alchemy, two Artificer’s Orbs, two runes, possibly two Exalted Orbs) since it holds up until level 33. The Bombard then takes over until 51: it’s the last one, so it might as well be excellent.

For the skill switch to go smoothly, gather this before touching the tree:

• At least two Gemcutters Prism, four if possible. This isn’t a comfort detail: the gap between two and four means double the damage. With none at all, don’t switch skills.
• One Greater Jewellers Orb for Flameblast (there’s a guaranteed one in the Nakanu zone of Act 4), plus a Lesser one for the grenade.
• A staff with +3 or +4 to fire spells and increased spell or fire damage. Check the vendors on every town visit from level 36 onward; as a last resort, gold lets you gamble for one.
• Between 30,000 and 35,000 gold for a full respec of the tree.
• Nine uncut support gems (seven at a pinch) and at least three uncut skill gems for Tornado, Frost Bomb and Elemental Weakness, plus one uncut spirit gem.

Weapon swap: the setup you cannot afford to get wrong

Two weapons, two skills, two sets of passive points: it’s the only genuinely technical piece of execution in this build, and getting it wrong costs you every point of damage.

The principle comes down to two lines. Weapon set 1 carries the staff and casts Flameblast; weapon set 2 carries the crossbow and casts Oil Grenade. In the skills panel, you need to open each skill and leave only its own set checked: set 1 for Flameblast, set 2 for Oil Grenade. The passive tree also has points specific to each set, to be allocated according to the written guide’s plan.

The penalty is brutal and silent: casting Flameblast with the crossbow equipped simply deals no damage at all, since everything comes from the staff. If your damage suddenly craters for no obvious reason, this is the first thing to check, before the gear, before the tree, before the gems.

Skill Tree