Lenswright's Cogitator
The Cogitator was first assembled by a clockmaker-turned-hedge-wizard named Arvel Prynn, who believed spellcasting was fundamentally a problem of imprecise calculation. She fitted a polished calcite lens into a rotating brass armature etched with logical proofs, then fed a binding sigil through its center. The device's peculiar hum has led those nearby to describe the uneasy feeling of being observed — as though the lens is cataloguing them.
Mechanics
A brass-and-crystal arcane focus that sharpens spellcasting by letting you reroll one damage die per spell and occasionally reveal hidden magical auras on command.
Refractive Channeling
This item functions as an arcane focus. When you cast a spell that deals damage and you roll a 1 on any single damage die, you may reroll that die once and must use the new result. This is a passive effect requiring no action and no resource.
Reveal the Invisible Lattice
As an action, you hold the Cogitator aloft and cause it to emit a pulse of pale amber light. Until the end of your next turn, any object or creature within 30 feet that bears an active magical effect, is under the influence of a spell, or carries an enchanted item causes the crystal to hum audibly and emit a faint glow visible to you only. This does not reveal the nature or school of the magic, only its presence and approximate location. This effect can be used 3 times, recharging all uses at dawn.
Theorem Lock
When you fail a concentration check (Constitution saving throw to maintain a spell), you may expend 1 use of Reveal the Invisible Lattice to reroll that saving throw, using the higher result. You must decide to use this before the DM declares whether the spell ends.
3 charges
Recharges at dawn
DM Notes
The Refractive Channeling passive is minor but satisfying — it prevents the sting of rolling a 1 on a key damage die without inflating average damage in any meaningful way. Reveal the Invisible Lattice is a soft detection tool, not a replacement for detect magic: it confirms presence but reveals no school or effect details, so DMs retain narrative control. Theorem Lock consumes the same charge pool as the detection ability, which creates a genuine resource tension — players must decide whether to conserve charges for concentration protection or spend them on exploration. At three charges total refreshing at dawn, Theorem Lock can be used at most three times per day, which is appropriate for an uncommon item. Avoid allowing this item to stack with Warcaster or Resilient (Constitution) in ways that trivialize concentration entirely; if the group already has those tools, the Theorem Lock sees diminished but still relevant use on unlucky streaks.
Generated with: Level 5 · Arcane focus · Heroic · Uncommon