Warlocks are among the most customizable classes in Dungeons & Dragons. In addition to a character's subclass, Warlocks are distinguished through their choice of Pact Feature and Eldritch Invocations, making every Warlock quite unique from each other. As Warlocks reach higher levels of the class, they gain access to a potent feature called Mystic Arcanum.
Mystic Arcanum is among the most powerful assets at any Warlock's disposal, so it's integral that players make the most out of this feature once it becomes available. So for newcomers interested in playing the Warlock class, we're going to explore everything you need to know about Mystic Arcanum.
What Is Mystic Arcanum?
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Traditionally, spellcasting-based classes like Clerics, Druids, and Wizards gain access to additional spell slots as they gain levels, gaining access to not just more spell slots, but slots of higher spell levels. Uniquely, despite being a full-fledged spellcasting class, Warlocks actually don't gain spell slots higher than fifth level. Though they don't have access to these higher-level spell slots, Warlocks are still capable of casting higher-level magic. Enter Mystic Arcanum.
Mystic Arcanum is a feature that first becomes available to Warlocks when they reach level 11 and is a powerful magical secret bestowed upon a character by their patron. This secret takes the form of one sixth-level spell that the Warlock at hand can cast once per long rest without the need to expend a spell slot.
In addition to this sixth-level Mystic Arcanum, a Warlock gains yet even more potent Mystic Arcanum options as they gain additional levels, gaining a seventh-level spell at level 13, one eighth-level spell at level 15, and one ninth-level spell at level 17.
The Ins And Outs Of Mystic Arcanum
As Warlocks are a class that is required to manage a very small pool of spell slots, access to Mystic Arcanum effectively provides not only even more powerful spell options that would normally be available to a character but more available instances in which they may cast a spell in a given battle as well.
It's important to note that while a Warlock's Mystic Arcanum can only be used once per long rest, each individual Arcanum that the character has access to is tracked separately. For example, if a level thirteen Warlock cast a spell using their sixth-level Mystic Arcanum, they could still access their seventh-level Arcanum.
Unfortunately, due to the way in which the Mystic Arcanum ability is worded, when a new Mystic Arcanum is gained, a Warlock is limited only to spells of that Arcanum's level. While this may seem obvious at first, it means that a Warlock couldn't opt to have a first-level spell up-cast to a sixth-level spell as one's first gained Mystic Arcanum.
Changing Mystic Arcanum
Thanks to the optional Eldritch Versatility feature introduced in Tasha's Cauldron of Everything, Warlocks actually have a means of changing their Mystic Arcanum. Once they gain access to Mystic Arcanum, on subsequent level-ups in which the Warlock can increase their ability scores such as level 12, a Warlock can opt to change one spell from their Mystic Arcanum feature. This means that if a Warlock isn't enjoying a spell they selected as much as they'd hoped, they can try out a different available option by simply gaining levels.