dnd 5e – What are Mythic Actions?

“Mythic Actions” are an optional rule given in Mythic Odysseys of Theros.

Unfortunately, usage guidance for Mythic Actions is not given in Van Richten’s Guide to Ravenloft, despite its having a creature with Mythic Actions. Usage guidance for Mythic Actions is found in chapter 6 of Mythic Odysseys of Theros, in the section “Mythic Monsters”:

Mythic traits transform battles into truly legendary confrontations, well suited to the climactic battles at the ends of adventures or whole campaigns. Mythic traits are optional; they don’t need to be used during combat with these monsters. If you so choose, you may simply ignore a monster’s mythic trait and mythic actions. If you wish to increase a battle’s stakes, though, using a monster’s mythic trait results in some mid-battle twist that changes the way the monster behaves, restores its resources, or provides it with new actions to use. As a result, the battle becomes deadlier and rages on for longer than most combat encounters. Each monster features an “As a Mythic Encounter” section that highlights its mythic trait, notes how using it changes the difficulty of the encounter and the rewards, and includes read-aloud text you can use mid-battle to signal a terrifying shift in the conflict.

This section in Theros goes on to give detailed guidance for using Mythic Actions for three of the monsters presented there; this guidance may be helpful for motivating the use of Mythic Actions with the Dullahan.