@spaceysnorlax As written, Mystic Arcanum doesn’t allow spells of lower levels, but a DM could certainly allow it.
How many times can a warlock use Mystic Arcanum?
The main reason Mystic Arcanum exists is that the game limits 6th-9th level spells to 1 per day and that idea isn’t compatible with how Pact Magic spell slots work. Mystic Arcanum literally says: You can cast your arcanum spell once without expending a spell slot. You must finish a long rest before you can do so again.
Does Mystic Arcanum count as spells known?
No, the warlock’s Pact Magic feature is a completely separate feature from the Mystic Arcanum feature, and each independently describes how you get spells without relying on or referring to the other. Pact Magic says you get another spell known at e.g. 11th level, so you do, period.
Can a warlock know more than one mystic Arcanum spell?
A spell you choose must be of a level no higher than what’s shown in the table’s Slot Level column for your level. The Slot Level column never increases above “5th”, so a warlock can never know a warlock spell of 6th level or higher. Therefore the Mystic Arcanum spells must be known separately from the warlock’s Pact Magic spells.
When do you regain your mystic Arcanum in raw?
That Mystic Arcanum usage could only be regained upon long rests, a la RAW. The Warlock would still only choose one spell per Mystic Arcanum that they learned. The Warlock would also be able to ‘upcast’ his lower level Mystic Arcanums, should they allow it (e.g. Create Undead, at level 9).
Where do you find spells known in Warlock?
The Spells Known column of the Warlock table shows when you learn more warlock spells of your choice of 1st level and higher. A spell you choose must be of a level no higher than what’s shown in the table’s Slot Level column for your level.
Is the Mystic Arcanum the same as Pact magic?
If that reasoning is not convincing, here’s a bit of circumstantial evidence underlining the necessary separation of the two features: Notice that the spells you gain access to with Pact Magic and Mystic Arcanum cannot be the same due to incompatible spell levels!
