[Radiance] Item - Hololight Prism

The precursor to arcane holographic devices, these carefully-crafted prisms refract arcane photon energy to produce magical illusory images. Some artificers can encode imperceptible imperfections into the crystal to produce custom illusions.

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Hololight Prism
Wondrous item, uncommon (requires attunement by a spellcaster)

This refracting prism can be used as a spellcasting focus. When you cast a spell through this prism and roll for damage, you can re-roll one die of your choice from each pair of matching damage dice results, if any. You must use the new results. Groups of three or more matching results do not count as a pair. If the spell rolls separate pools of dice for damage, such as each ray of the scorching ray spell, pairs are selected from all damage dice rolled for that spell, collectively.

Lumemancy Refraction. When you use this prism to cast a spell that produces light, you can choose to refract the light produce magical images instead. Your spell's effect is replaced by that of a different spell described below. The effect is determined by the level of the original spell.

• Cantrip. If you refract a light-producing cantrip, such as light or dancing lights, your spell instead produces the effect of a minor illusion cantrip.

• 1st-level or 2nd-level Spell. If you refract a light-producing 1st-level or 2nd-level spell, such as color spray or faerie fire, your spell instead produces the effect of a silent image spell.

• 3rd-level or Higher Spell. If you refract a light-producing spell of 3rd-level or higher, such as daylight, your spell instead produces the effect of a major image spell.

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Imprinted Message Variant. Master glassworkers or transmutation mages can produce special prisms encoded with messages that can only be revealed by passing magical light through it. When you refract a spell using the prism’s Lumemancy Manipulation property, the prism’s new spell effect instead displays an illusion pre-programmed by the prism’s maker, as if the maker had cast that illusory spell. Thus, a single prism can be encoded with up to three messages this way, each revealed by spells of different levels.

Over the course of a short or long rest, a character proficient in both Arcana and glassblower's tools can expend 15 gp worth of materials and a spell slot of an appropriate level to modify any encoded message of choice from a hololight prism. The level of the expended spell slot must equal the spell level associated with the message you modify.

Additionally, a small picture or a short written message no longer than 25 words can also be encoded into the prism, designed to be revealed by nonmagical light such as candlelight. Because it is nonmagical, modifying this short message does not require expending spell slots.

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DESIGN COMMENTARY

A light/radiance-based theme would be incomplete without an item that explores prisms and splitting light. The raybreaker item from Unearthed Gems fits this perfectly, but I also had a different idea in mind.

The hololight prism incorporates a fun mechanic that allows you to "split" pairs of dice rolls. It's not mechanically significant, since if you roll many dice you're more likely to receive triples, and you wouldn't re-roll high-result pairs (occurs half the time). It's most effective for mid-level spells, elevating their damage. It's best paired with spells that roll 2-4 dice, such as cantrips past 5th-level, a 2nd-level scorching ray, or an appropriate magic missile. Overall, the average damage increase is maybe only 10-40 extra damage per day, truly dependent on the spell choice.

The prism's other feature basically expands your spell list. You still expend your spell slots as normal. It's a rather minor benefit overall.

The imprinted message variant is primarily a roleplay and exploration variant. It is less of an item for players and more for NPCs who are sending secret messages to players. The modification requirements (glassblowers tools and Arcana) makes it generally unlikely player characters will be able to modify it. This item would be well-suited to secret organizations such as a rogues guild or the assassin-artisan guild Master Artisans from the Tools of the Trade compendium.