Warlocks, something something, over/underpowered?

[JakOfAllTirades]

Odd question: can a warlock choose a spell of 5th or lower level as one of his arcana, for the purposes of once/day upcasting?

This may be possible according to RAW, due to the rules for upcasting a spell. When a spellcaster casts a spell using a slot that is o f a
higher level than the spell, the spell assumes the higher level for that casting. (PHB p201) So by that rule, "a 6th level spell from the Warlock spell list" could be any Warlock Spell of 6th level or lower, upcast to 6th level.

The rules for Mystic Arcanum also say you can cast the spell once per day without using a spell slot. So now I'm not so sure. If it doesn't have a spell slot, is it possible to use an upcast spell at all? But then, if it's possible to cast a 6th level non-upcast spell without a spell slot, why not an upcast one as well?

Unless it breaks the game, I'd probably allow it.

[tieren]

This may be possible according to RAW, due to the rules for upcasting a spell. When a spellcaster casts a spell using a slot that is o f a
higher level than the spell, the spell assumes the higher level for that casting. (PHB p201) So by that rule, "a 6th level spell from the Warlock spell list" could be any Warlock Spell of 6th level or lower, upcast to 6th level.

The bolded part is the RAW reason this can't happen, an upcast spell is only a spell of that level at the time of casting. You choose the arcanum when you level up which is probably not i the middle of casting, and as you note thre is no way for a warlock to upcast to 6th level without a 6th level slot.

Put another way, in order for a lower level spell to be considered a 6th level spell, you have to be in the process of casting it (at 6th level) in order to select it as an arcanum, and that is impossible since you don't have a 6th level slot to cast it with.

[Dalebert]

I agree it's not RAW but in Homebrews I allow warlocks to pick a lower level spell cast at level X for their Mystic Arcanums. It's limited enough as it is versus other casters.

[JakOfAllTirades]

The bolded part is the RAW reason this can't happen, an upcast spell is only a spell of that level at the time of casting. You choose the arcanum when you level up which is probably not i the middle of casting, and as you note thre is no way for a warlock to upcast to 6th level without a 6th level slot.

Put another way, in order for a lower level spell to be considered a 6th level spell, you have to be in the process of casting it (at 6th level) in order to select it as an arcanum, and that is impossible since you don't have a 6th level slot to cast it with.

Fair enough. Good catch.

[Pharaon]

I'm not suggesting he melt down his 6-9 spell slots, I'm suggesting he melt down his 1-4 spell slots. Once he has his full complement of 1-4 spell slots at level 9, he can trade them all in for a total of 41 sorcery points. Along with his natural sorcery points, he has 50 total, which he can turn into 7 level 5 spell slots

So at level 9 he can cast 8 level 5 spells a day. At level 10 that becomes 9, at level 15 that becomes 10 and at level 18 that becomes 11. And then yes, the Sorcerer gets an extra level 6 and 7 slot at levels 19 and 20 that the warlock doesn't get, so let's call it 13.

This is largely academic, a means of comparing apples to apples.

I'd like to dispute the math here. Unless I'm much mistaken, melting down all level 1-4 spell slots from 9 onwards should only net you 31 sorcery points, not 41. Then add class level for a total of 40 (at level 9).

Spoiler: Math

Show

4*1=4
3*2=6
3*3=9
3*4=12
4+6+9+12=31

This significantly alters the ramifications. Our level 9 sorcerer would have 6 slots of 5th level, 7 slots at level 10 (warlocks are notably weak from 8-10, so this isn't surprising), 8 at level 11 (when the averagely-rested warlock would have 9 slots), and 10 slots at level 18 (while our warlock has 12 slots for 5th level spells starting at 17).

While this ignores the sorcerer's clear advantage in 6th-to-9th level spells, it also ignores that the above calculation consumes most-or-all of a sorcerer's long rest resource and none of a warlock's long rest resources.