In the adventure Critical Role: Call of the Netherdeep, characters are bound to come across the otherworldly material known as ruidium. This alien mineral imbues its twisted energy into things it touches. While it isn’t guaranteed when the players will first encounter ruidium, one thing is for sure: its discovery will present their characters with unique challenges.

The full extent of ruidium’s role in Call of the Netherdeep is still under wraps, but let’s take a look at what we know about it and its double-edged potential. Players beware, spoilers for Call of the Netherdeep lie ahead!

• What is ruidium?
• How ruidium corruption works
• Magic item preview: Ring of red fury

What is ruidium?

Ruidium is described as a “slick, oily stone veined with blood-like streaks” that forms in crystalline structures that run through the sunken caverns of the Netherdeep. This mineral got its name from its similarities in color to the second Exandrian moon, Ruidus.

Not much is known about ruidium beyond that it is powerfully magical. Since its discovery, different scholarly factions have been at odds trying to secure a steady supply for research. 

Ruidium’s properties are yet to be fully realized, but initial research of the mineral shows it can spread its crystalline structure into both organic and inorganic substances. The chances of spread are greatly increased when creatures or objects remain in prolonged contact with it.

Ruidium items

Magical items can be infused with ruidium to become even more powerful, and even mundane items develop magical properties after sufficient exposure. It goes without saying that the scholarly factions investigating ruidium would have great use for a party of adventurers that are able to get a hold of ruidium items. 

While ruidium might seem like an obvious blessing from the mysterious realm of the Netherdeep, ruidium items do not come without their downsides. When used for too long, items that have been infused by ruidium spread their crystalline structure to the creatures that wield them. This process, called ruidium corruption, starts with physical effects but can also cause psychological distress in cases that have progressed beyond the initial stages.

How ruidium corruption works

The first physical sign of ruidium corruption is a bright red rash that appears on the creature’s body where it made contact with the ruidium. Due to its debilitating effects on a creature’s body, ruidium exposure also causes creatures to gain levels of exhaustion.

Creatures that are exposed to ruidium multiple times show increasingly serious symptoms of ruidium corruption, coinciding with the creature’s level of exhaustion:

Source: Call of the Netherdeep

Roleplaying ruidium corruption

While minor physical characteristics might be easy to ignore, ruidium corruption can also twist a creature's mind. A creature experiencing ruidium corruption may display signs of emotional distress that progressively worsen as the corruption spreads. The psychological symptoms of ruidium corruption include increased feelings of regret, yearning, rage, and despair. 

When a character gains a level of ruidium corruption, it can be helpful for the Dungeon Master and player to decide how this will affect the character. A couple examples to roleplay ruidium corruption could be:

• Adding a flaw to the character’s flaws
• Emphasizing or expanding upon a current flaw

Curing ruidium corruption

Characters exposed to ruidium may seek to remedy themselves of this body and mind-altering substance. Unfortunately, there is no known cure beyond a wish spell or divine intervention. 

While this may seem bleak for characters that have advanced ruidium corruption, there is one upside–ruidium corruption only progresses with exhaustion levels. Taking a couple of days off to get some long rests can cure a character of their exhaustion and buy them some time to discover a cure. Keep in mind that the physical and mental characteristics of ruidium corruption remain even when the exhaustion is cured.

Homebrewing ruidium cures

Dungeon Masters can find themselves in a tricky spot when multiple party members develop advanced cases of ruidium corruption. If you’re having trouble balancing ruidium corruption at your table, consider the following ideas:

• A powerful cleric may be able to help those with ruidium corruption by seeking a deity's help on behalf of a corrupted character. This service can be acquired by a sufficient donation to the church, or by the party performing an adequate favor. 
• A scholarly faction, like the Library of the Cobalt Soul, may be able to formulate a cure or way to suppress the effects of ruidium corruption if the party is in good standing with the organization.
• Instead of exhaustion, characters could sacrifice other resources to keep ruidium corruption at bay. For spellcasters, this might come in the form of spell slots. Martial characters, on the other hand, might sacrifice some of their Constitution score.

Magic item preview: Ring of red fury

Below is a look at the ruidium item ring of red fury from Critical Role: Call of the Netherdeep.

Ring of Red Fury

Very rare (requires attunement)

This ring has a stripe of ruidium running through it. While wearing the ring, you gain the following benefits:

• You can breathe water.
• You gain a swimming speed equal to your walking speed.

Ruidium Rage. As a bonus action, you can use the ring to gain the following benefits, which last for 1 minute or until you are incapacitated:

• You have advantage on Strength checks and Strength saving throws.
• When you hit with an attack, you can add your proficiency bonus to the damage roll.
• Difficult terrain doesn’t cost you extra movement, and you are immune to the paralyzed and restrained conditions.

You can’t use this property of the ring again until you finish a long rest.

Ruidium Corruption. When you use the Ruidium Rage property of the ring, you must make a DC 20 Charisma saving throw. On a failed save, you gain 1 level of exhaustion. If you are not already suffering from ruidium corruption, you become corrupted when you fail this save.

Source: Call of the Netherdeep

Fighters and monks, who can make more attacks per round than any other class, will make especially good use of this item by adding their proficiency bonus to each damage roll. The one downside for those classes is that they would be particularly susceptible to failing the Charisma saving throw and gaining a level of exhaustion and exposing themselves to ruidium corruption. 

A warlock, on the other hand, will be able to use this item in conjunction with their eldritch blast to pump out a lot of damage. Seeing as they get proficiency with Charisma saving throws and will most likely have a high Charisma modifier, the Charisma saving throw will be a lot less scary than for other classes. 

Will ruidium bring you glory or ruin?

Critical Role: Call of the Netherdeep will set adventurers against all sorts of challenges and creatures. Ruidium may be your best chance to combat these perils, but at what cost? You can find out when the adventure drops on March 15!

Mike Bernier (@arcane_eye) is the founder of Arcane Eye, a site focused on providing useful tips and tricks to all those involved in the world of D&D. Outside of writing for Arcane Eye, Mike spends most of his time playing games, hiking with his girlfriend, and tending the veritable jungle of houseplants that have invaded his house.