Overview
This Gemling Legionnaire build turns Spark into a trigger engine. Spark itself handles clearing — projectiles pierce through packs and blanket the screen — but its real job is generating the hit frequency that feeds Cast on Critical. Every time a Spark crit lands, Comet drops on top of the target, which is where the build’s actual damage comes from.
Archmage is the scaling backbone. Mana investment converts straight into spell damage, so gearing pushes mana pool and mana sustain as hard as it pushes lightning and spell damage. That gives the build a long progression curve: it works as a plain Spark caster early, then transforms once crit consistency, Cast on Critical and Archmage all come online together.
Around that core sits a wide utility kit — Frost Bomb, Orb of Storms, Fireball and Elemental Conflux for extra elemental pressure, plus recovery and defensive tools to keep the engine running through longer fights. It is a build for players who enjoy layered caster setups rather than a single-button rotation.
Pros & Cons
Pros
- Screen-wide Spark clear that makes mapping fast and hands-off
- Cast on Critical Comet delivers large automatic burst against rares, elites and bosses
- Scales aggressively with mana, crit stats, cast speed and gear investment
- Deep utility kit covers exposure, shock and extra elemental pressure when packs get tanky
- Ranged playstyle keeps you out of danger while the trigger setup does the damage
Cons
- Weak until the full engine is assembled — early on it is just a basic Spark caster
- Low crit chance makes Comet triggers inconsistent and the damage feels flat
- Poor mana sustain makes Spark clunky and breaks the whole loop
- Defensive layers still need deliberate investment; the build does not tank for you
Key Skills
- Spark — main clear skill and the hit generator for the trigger setup, supported with Pierce, Execute and projectile scaling
- Cast on Critical + Comet — the burst engine, with Spell Cascade widening Comet coverage
- Archmage — converts mana investment into spell damage; the primary scaling lever
- Clarity — mana sustain so Spark can be cast continuously
- Frost Bomb / Orb of Storms / Fireball — elemental utility for exposure, shock and extra pressure on tanky targets
Gear & Anointments
Prioritise lightning damage, spell damage, critical chance and critical damage, cast speed, mana and mana sustain, projectile speed, cooldown recovery and defensive layers. Mana sits alongside damage as a top priority because Archmage scales off it directly. Cast speed pulls double duty — more projectiles means both better screen coverage and more chances to roll a crit and trigger Comet. Elemental Conflux, Sigil of Power and Virtuous Barrier round out the utility slots. Specific uniques and anointments to be confirmed against the source video.
Endgame Notes
Mapping is the build’s best content — Spark saturates the screen and Comet triggers delete anything that survives the initial wave. Bossing holds up well once crit is consistent: stay at range, keep Spark uptime high, and let the automatic Comets accumulate rather than trying to force damage windows. The build keeps improving with investment, so it suits players planning to min-max into deeper endgame content.
Credits & Source
Build credited to RNGenius. See the source video for the full build’s gameplay footage + voice commentary: SPARK CAST ON CRITICAL COMET GEMLING LEGIONNAIRE BUILD GUIDE | POE 2 PATCH 0.5.