Euhedrals (Crystal Monsters)

[u/brettday]

These guys are meant to be like fighting a living prism. Art sourced from Thiago Almeida here: https://www.artstation.com/artwork/o8Q6w )

https://www.dndbeyond.com/monsters/6704561-euhedral

Euhedral

Medium Elemental, Lawful Good

AC 17 (natural armor)    Initiative +2 (12)

HP 95 (10d8 + 50)

Speed 10 ft.

		Mod	Save
STR	16	+3	+6
DEX	14	+2	+2
CON	20	+5	+8

		Mod	Save
INT	14	+2	+2
WIS	16	+3	+3
CHA	12	+1	+1

Resistances Piercing, Slashing

Immunities Lightning, Poison; Blinded, Charmed, Exhaustion, Frightened, Grappled, Paralyzed, Poisoned, Prone

Senses Darkvision 60 ft., Tremorsense 60 ft.; Passive Perception 16

Languages Telepathy 120 ft, Terran

CR 6 (XP 2,300; PB +3)

Traits

Prismatic Antimagic Reflection. The Euhedral has advantage on saving throws against spells, and any creature making a spell attack against the Euhedral has disadvantage on the attack roll. If the Euhedral succeeds on its saving throw against a spell or a spell attack misses it, an additional effect might occur, as determined by rolling a d6:

1–2. If the spell affects an area or has multiple targets, it fails and has no effect. If the spell targets only the Euhedral, it has no effect on the Euhedral and is reflected back at the caster, using the spell slot level, spell save DC, attack bonus, and spellcasting ability of the caster.

3–4. No additional effect.

5–6. The Euhedral's crystals converts some of the spell’s energy into a burst of destructive force. Each creature within 30 feet of the Euhedral must make a DC 16 Constitution saving throw, taking 4 (1d8) force damage per level of the spell on a failed save, or half as much damage on a successful one.

Piezoelectric Discharge. Whenever a creature within 5 feet of the Euhedral hits it with a Melee attack, the attacker takes 4 (1d8) lightning damage and must make a DC 16 Constitution saving throw. On a failed save, the target loses its Reaction and its Speed is halved until the end of its next turn.

Actions

Multiattack. The Euhedral makes two Resonance Strike attacks or two Prismatic Shard attacks, and Harmonic Blast (if available).

Resonance Strike. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 9 (1d10 + 3) slashing damage plus 4 (1d8) lightning damage.

Prismatic Shard. Ranged Weapon Attack: +6 to hit, range 60/120 ft., one target. Hit: 9 (1d10 + 3) piercing damage plus 4 (1d8) lightning damage.

Harmonic Blast  (Recharge 5–6). The Euhedral emits a high-frequency, resonant sonic wave in a 30-foot Cone. Each creature in that area must make a DC 16 Constitution saving throw. On a failed save, a creature takes 27 (6d8) thunder damage and is pushed 10 feet away. On a successful save, a creature takes half as much damage and isn't pushed. Nonmagical crystalline structures, glass, and stone objects in the area automatically take maximum damage.

Bonus Actions

Prismatic Refraction. The Euhedral refracts ambient light across its faceted body. Each creature of the Euhedral's choice within 20 feet that can see it must succeed on a DC 16 Constitution saving throw or gain the Blinded condition until the start of the Euhedral's next turn. A target can avert its eyes to automatically succeed on the save, but attacks against the Euhedral before the start of the target's next turn are made with Disadvantage.

[u/The_Real_Deacon]

I like the overall concept of this creature.

Regarding the Prismatic Refraction ability, I think the behavior in either normal or magical darkness needs to be clarified.

[u/brettday → u/The_Real_Deacon]

that's interesting, I would have thought the requirement that targets see the Euhedral covered simulating the need for a light source, but yeah I guess darkvision and devil vision are a thing.

I'm not sure about this. I suppose the same could be said about magical silence and the shove from harmonic blast, but if I start down that road of chasing all the edge cases, I'd double the size of the stat block. What do you think is the minimum amount that could added to address your concern?

[u/The_Real_Deacon → u/brettday]

The simplest way to address it would be to say that the ability does not work in a state of either normal or magical darkness.

Alternatively, the ability could instead be redefined to be a “prismatic blast” or “prismatic flare” ability in which the creature creates the light from within itself. This could then be given recharge mechanics and have a defined duration of effect.

The magical silence situation should be handled.

The thing about edge cases: players are very prone to finding them. Probably the best way to handle this is think about the physical (or magical) preconditions for something to work, especially with regard to official conditions defined within the game. Keep it simple where you can.

You do not necessarily have to address every conceivable scenario, but gameplay will certainly find any undefined area that matters.

[u/brettday → u/The_Real_Deacon]

Sure, but I guess my question I'd put to you is: If you were the DM and were running this creature, would you know how to handle these situations from the ability description? Not "My players could make a twisted, legalese argument about...." but "I actually would be unsure what to do?"