Eureka Criterion
Built over the course of a single sleepless week in a cluttered workshop, the Eureka Criterion began as a question scrawled on a chalkboard: what if a weapon could think faster than the hands that held it? Its maker never considered it finished — every version was merely the best available draft — and the crossbow reflects that restless perfectionism in the way it hums, recalibrates, and occasionally ejects spent bolts with unnecessary enthusiasm. The glyphs it leaves behind are written in a personal shorthand only its creator fully understands, which she considers a feature, not a flaw.
Mechanics
A self-loading precision crossbow that accumulates Theorem Points through combat discoveries, unleashing escalating effects as its wielder solves the battlefield's problems with elegant lethality.
Theorem Engine — 6 charges, recharges 1d4+2 at dawn
The Eureka Criterion has 6 charges used to power its abilities. It regains 1d4+2 expended charges each dawn. The crossbow does not require a free hand to load — it loads automatically as part of the attack, and its rate of fire is limited only by the action economy of normal attacks. It deals 1d10 piercing damage on a hit.
Annotated Shot
When you make an attack roll with this crossbow and hit, you may expend 1 charge as part of that attack (no additional action required) to embed a luminous theoretical glyph in the target. The first time that target is hit by any attack before the start of your next turn, the attacker deals an additional 2d10 force damage and the glyph detonates, extinguishing itself. A creature can have only one Annotated glyph on it at a time.
Field Hypothesis
As a bonus action, you may expend 2 charges to project a crackling hypothesis field in a 10-foot radius centered on a point you can see within 60 feet. The field lasts until the start of your next turn. Creatures of your choice within the field when it appears must succeed on a DC 18 Constitution saving throw or have their speed halved until the end of their next turn. Allies within the field gain advantage on the next attack roll they make before the field expires, as the field highlights weak points in a flash of diagnostic light.
Ballistic Theorem
As an action, you may expend 3 charges to fire a convergence bolt that ricochets between up to 4 targets you can see within 60 feet of each other, beginning with a primary target within 120 feet of you. Make a separate attack roll against each target. On a hit, each target takes 3d8 piercing damage plus 3d8 force damage. Each successive target after the first grants a cumulative +2 bonus to that attack roll (so the second target is at +2, the third at +4, the fourth at +6), as the bolt refines its trajectory with each impact.
Perfect Iteration
Once per dawn, when you roll damage with this crossbow and dislike the result, you may declare Perfect Iteration before any other effect resolves. Reroll all damage dice from that attack. You must use the new result. This reflects the wielder's compulsion to get things exactly right — and the crossbow's willingness to cooperate.
The Final Proof
Once per dawn, as an action, you may expend 5 charges to fire a single bolt that compiles every Annotated glyph, active Field Hypothesis, and residual Ballistic Theorem trajectory in a 60-foot line originating from you. Every creature in the line must succeed on a DC 18 Dexterity saving throw or take 8d10 force damage, or half on a success. The line's width is 5 feet. The crossbow then enters a cool-down state and cannot use charges until your next dawn recharge, though it still functions as a normal +2 light crossbow during this time.
6 charges
Recharges 1d4+2 at dawn
DM Notes
Balance consideration: The Final Proof is a high-burst nova ability that deals up to 80 force damage on a failed save in a 60-foot line — roughly equivalent to a 9th-level spell in raw output. Its trade-off is the charge lock-out and the once-per-dawn restriction, so the DM should ensure the party cannot trivially rest between every major encounter. Ballistic Theorem at 3 charges targets up to 4 creatures with separate attack rolls, which at level 17 represents strong sustained multi-target damage — monitor closely in encounters with 3+ clustered enemies. Annotated Shot rewards coordinated party play and is intentionally the cheapest ability to encourage frequent use without feeling wasteful. The +2 attack and damage bonus (implicit in the weapon's base profile referenced in The Final Proof fallback mode) should be noted as standard for a Legendary weapon. This item is best suited to an Artificer who leans into tactical positioning and planning rather than brute force — reward that mindset by populating encounters with clustered enemies and multiple viable targets.
Generated with: Level 17 · Artificer · Artillerist · Weapon · A theme that fits her character · Heroic · Legendary · No curses