But, they did. They said you can cast the spell False Life. And when a Warlock casts a spell, they cast it at the level according to the table...
Look at One With Shadows. When a Warlock casts Invisibility using a spell slot, they cast it at a higher level which would mean that they could cast it on others. If your interpretation is true, and that a spell cast from an Invocation was only cast at the lowest possible level, then there'd be absolutely no need for the wording in the invocation that limited the spell to the Warlock. It'd be totally unnecessary and redundant. The same is true with Otherworldly Leap.If it were already the case that the spell from the invocation could only be cast at its lowest level, then there'd be no need for the wording in this invocation that limited the spell to the Warlock. Again, it would be totally unnecessary and redundant. Why would they put that wording in, if it were not necessary to change the way the spell cast via the invocation worked? This is clear indication of intent.
I think that the other two invocations are clear evidence that the RAI is for spells cast via the invocations are cast at the same spell level as the Warlock's slots indicate, as if they were casting it normally with a spell slot, unless otherwise restricted by the wording in the invocation. I.E. False Life is cast without a spell slot at the same level as if it were being cast using a spell slot, while Invisibility and Jump are being cast at their lowest level because of the wording that specifically limits the spells to the Warlock themselves.
No with Fiendish Vigor you can cast False Life on yourself without expending a spell slot.
Per official ruling in Sage Advice Compendium; unless the text says otherwise, a spell cast without a spell slot is cast at its lowest possible level, which is the level that appears in its description.
The spell False Life is Level 1 in its description and Fiendish Vigor text doesn't say otherwise.
What level is a spell if you cast it without a spell slot?
Unless the text says otherwise, a spell cast without a spell slot is cast at its lowest possible level, which is the level that appears in its description.
An example of an exception to this is often found in monster stat blocks. A monster with the Spellcasting action may have spells listed with a “(level # version)” parenthetical. This means the spell is still cast without a spell slot, but its effects are equivalent to a version of the spell cast using a spell slot of the specified level.
Look at One With Shadows. When a Warlock casts Invisibility using a spell slot, they cast it at a higher level which would mean that they could cast it on others. If your interpretation is true, and that a spell cast from an Invocation was only cast at the lowest possible level, then there'd be absolutely no need for the wording in the invocation that limited the spell to the Warlock. It'd be totally unnecessary and redundant. The same is true with Otherworldly Leap.If it were already the case that the spell from the invocation could only be cast at its lowest level, then there'd be no need for the wording in this invocation that limited the spell to the Warlock. Again, it would be totally unnecessary and redundant. Why would they put that wording in, if it were not necessary to change the way the spell cast via the invocation worked? This is clear indication of intent.
I think that the other two invocations are clear evidence that the RAI is for spells cast via the invocations are cast at the same spell level as the Warlock's slots indicate, as if they were casting it normally with a spell slot, unless otherwise restricted by the wording in the invocation. I.E. False Life is cast without a spell slot at the same level as if it were being cast using a spell slot, while Invisibility and Jump are being cast at their lowest level because of the wording that specifically limits the spells to the Warlock themselves.
You seem to be under the impression that Invisibility and Jump can only be cast on the caster themselves when cast at their base level, which is not the case. Both spells can be cast on any creature the caster touches. It's limited to one creature at the lowest level, but that one creature doesn't have to be the caster.
Spell Slots. The Warlock Features table shows how many spell slots you have to cast your Warlock spells of levels 1–5. The table also shows the level of those slots, all of which are the same level. You regain all expended Pact Magic spell slots when you finish a Short or Long Rest.
For example, when you’re a level 5 Warlock, you have two level 3 spell slots. To cast the level 1 spell Witch Bolt, you must spend one of those slots, and you cast it as a level 3 spell.
This does not say all Warlock spells are cast at the level according to the Warlock Features Table, what it actually says is that when a Warlock casts a spell using a Pact Magic Spell Slot, they cast it at the level of the Warlock Features Table. In this case, you're not expending a spell slot and thus do not get to upcast it. In fact Fiendish Vigor doesn't even prepare the spell, so the only method it gives you to cast False Life is via the Invocation itself and that specifically does not expend a spell slot.
But, they did. They said you can cast the spell False Life. And when a Warlock casts a spell, they cast it at the level according to the table...
Look at One With Shadows. When a Warlock casts Invisibility using a spell slot, they cast it at a higher level which would mean that they could cast it on others. If your interpretation is true, and that a spell cast from an Invocation was only cast at the lowest possible level, then there'd be absolutely no need for the wording in the invocation that limited the spell to the Warlock. It'd be totally unnecessary and redundant. The same is true with Otherworldly Leap.If it were already the case that the spell from the invocation could only be cast at its lowest level, then there'd be no need for the wording in this invocation that limited the spell to the Warlock. Again, it would be totally unnecessary and redundant. Why would they put that wording in, if it were not necessary to change the way the spell cast via the invocation worked? This is clear indication of intent.
I think that the other two invocations are clear evidence that the RAI is for spells cast via the invocations are cast at the same spell level as the Warlock's slots indicate, as if they were casting it normally with a spell slot, unless otherwise restricted by the wording in the invocation. I.E. False Life is cast without a spell slot at the same level as if it were being cast using a spell slot, while Invisibility and Jump are being cast at their lowest level because of the wording that specifically limits the spells to the Warlock themselves.
As Athanar pointed out, if you were correct, then the spells from arcane grimoire would be undercast, which obviously makes no sense.
Look at One With Shadows. When a Warlock casts Invisibility using a spell slot, they cast it at a higher level which would mean that they could cast it on others. If your interpretation is true, and that a spell cast from an Invocation was only cast at the lowest possible level, then there'd be absolutely no need for the wording in the invocation that limited the spell to the Warlock. It'd be totally unnecessary and redundant.
invisibility is a Touch spell, not a Self spell, so language limiting the warlock to only being able to cast it on themselves is absolutely not "unnecessary and redundant"
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Active characters:
Edoumiaond Willegume "Eddie" Podslee, Vegetanian scholar (College of Spirits bard) Lan Kidogo, mapach archaeologist and treasure hunter (Knowledge cleric) Mardan Ferres, elven private investigator (Assassin rogue) Peter "the Pied Piper" Hausler, human con artist/remover of vermin (Circle of the Shepherd druid) Xhekhetiel, halfling survivor of a Betrayer Gods cult (Runechild sorcerer/fighter)
RAW any Warlock who takes the Eldritch Invocation Fiendish Vigor should replace it at Level 6 with the EI Lessons of the First Ones and take the Tough Feat. Assuming we cannot upcast False Life using the EI, you will only ever get 12 Temporary Hit Points out of it. If you take Tough instead, you get 12 Hit Points at Level 6, non-temporary, and you can have additional THP on top of that, and it scales with your level, which is better. You could make the argument that you could use Fiendish Vigor to cast False Life as an action during combat, but I honestly don't see that ever being the best option a Warlock has at 6th level or higher because they'd be giving up 2 Eldritch Blast or Pact Weapon attacks or a leveled spell (minimum 3rd level spell from Pact Magic, or a Mystic Arcanum). The opportunity cost of casting False Life at first level in combat increases significantly as you get to higher levels.
None of the other invocations are as easily outclassed or outright replaced as Fiendish Vigor. At first glance Master of Myriad Forms seems to replace Mask of Many Faces... until you realize that Alter Self requires concentration, which severely limits its usefulness by imposing an opportunity cost. No Hex or Suggestion while altered, for instance. Witch Sight similarly seems to replace Visions of Distant Realms... but you can't use Witch Sight to see places other than where you are, while the Arcane Eye spell can be moved around to see distant or hidden places. For each of these pairs of invocations, there is a genuine trade off that could be significant to gameplay. This is not the case for Fiendish Vigor because its only theoretical leg-up over the Tough Feat is that it could be cast during combat... which is basically never going to be anywhere close to the best option a Warlock has due to the incredible opportunity cost of giving up your Action for the turn. To say nothing of the fact that by Level 12, the Tough Feat essentially accounts for 2 Actions' worth of False Life casts AND you can have other THP AND the opportunity cost to cast it even once is now 3 Eldritch Blast attacks or 3 Pact Weapon attacks or a 5th Level Pact Magic cast or a 6th Level Mystic Arcanum.
Fiendish Vigor is straight up useless after a certain point in a way that the other Eldritch Invocations aren't... assuming that the RAI is that it should always be cast at 1st Level.
Looking at it from the other potential RAI perspective where the cast of False Life scales with your Pact Magic spell level because it is considered a Warlock Spell, Fiendish Vigor is suddenly much more viable. It outpaces Tough in terms of total HP until level 16, even assuming no in-combat casts, but it has the drawback of not being able to benefit from other THP sources like Dark One's Blessing, Inspiring Leader, or Rally. If you do decide to use it in combat, it's no longer the worst option in the world. 32 THP is significant, but by the time you're 16th level and fighting (presumably) roughly CR 16 creatures, you'll potentially be taking 60+ damage from an Adult Dragon's Breath Weapon. In a single turn. Using your whole Action to give yourself 32 THP is not broken at that point, but could certainly be the difference between death and survival in a non-negligible amount of situations.
In addition, other features that give a caster a spell to cast at will specify that casting at a higher level requires a higher level slot, while Fiendish Vigor does not. Examples are the Wizard's Spell Mastery and Signature Spells. This lends credence to the claim that the absence of this specification is intentional.
I believe RAI, Fiendish Vigor should scale with Pact Magic, because otherwise it is unimaginably bad in a way that none of the other Eldritch Invocations are. It's a straight-up balance issue. Where the Warlock is constrained in terms of quantity of spells it can cast, it flourishes in the flexibility and modularity it is afforded through the Eldritch Invocations. To that end, I would argue that all of the Eldritch Invocations should be viable at as many levels of play as possible.
If I were to rewrite the EI to reflect that balance and clear up confusion, the first sentence would read as "You can cast False Life on yourself at the level of your Pact Magic spell slots without expending a spell slot." If you decide that's fun for you, please steal that idea. If you decide it's not, then don't.
Fiendish Vigor should only really be replaced if you have a better form of temporary HP. Tough for 12 HP at level 6 won't go as far.
Consider you're an archfey warlock with Pact of the blade at level 6, you make three attacks using PAM and after your turn you are hit for 8 damage. You use Misty escape to cast misty step with dreadful step and move back behind the party frontliners.
After the combat you're 8 hp down, with tough that is just 8 hp gone while with fiendish vigor you just recast it and that 8thp is back at no resource cost. As a pact of the blade warlock, you're more at risk of taking damage and so that 12 thp over the course of 4 encounters could be the same as up to 48hp, tough isn't touching that.
Now as temporary HP does not stack, if you have other forms of temporary HP, such as the inspiring leader feat, that maybe where you consider getting rid of fiendish vigor.
No with Fiendish Vigor you can cast False Life on yourself without expending a spell slot.
Per official ruling in Sage Advice Compendium; unless the text says otherwise, a spell cast without a spell slot is cast at its lowest possible level, which is the level that appears in its description.
The spell False Life is Level 1 in its description and Fiendish Vigor text doesn't say otherwise.
As others have pointed out, there is nothing in the rules that says this anywhere.
You seem to be under the impression that Invisibility and Jump can only be cast on the caster themselves when cast at their base level, which is not the case. Both spells can be cast on any creature the caster touches. It's limited to one creature at the lowest level, but that one creature doesn't have to be the caster.
pronouns: he/she/they
Others have already rebuked this point but I just want to point to the very area I reckon you got this incorrect idea from:
https://www.dndbeyond.com/sources/dnd/phb-2024/character-classes-continued#Level1PactMagic
This does not say all Warlock spells are cast at the level according to the Warlock Features Table, what it actually says is that when a Warlock casts a spell using a Pact Magic Spell Slot, they cast it at the level of the Warlock Features Table. In this case, you're not expending a spell slot and thus do not get to upcast it. In fact Fiendish Vigor doesn't even prepare the spell, so the only method it gives you to cast False Life is via the Invocation itself and that specifically does not expend a spell slot.
As Athanar pointed out, if you were correct, then the spells from arcane grimoire would be undercast, which obviously makes no sense.
invisibility is a Touch spell, not a Self spell, so language limiting the warlock to only being able to cast it on themselves is absolutely not "unnecessary and redundant"
Active characters:
Edoumiaond Willegume "Eddie" Podslee, Vegetanian scholar (College of Spirits bard)
Lan Kidogo, mapach archaeologist and treasure hunter (Knowledge cleric)
Mardan Ferres, elven private investigator (Assassin rogue)
Peter "the Pied Piper" Hausler, human con artist/remover of vermin (Circle of the Shepherd druid)
Xhekhetiel, halfling survivor of a Betrayer Gods cult (Runechild sorcerer/fighter)
RAW any Warlock who takes the Eldritch Invocation Fiendish Vigor should replace it at Level 6 with the EI Lessons of the First Ones and take the Tough Feat. Assuming we cannot upcast False Life using the EI, you will only ever get 12 Temporary Hit Points out of it. If you take Tough instead, you get 12 Hit Points at Level 6, non-temporary, and you can have additional THP on top of that, and it scales with your level, which is better. You could make the argument that you could use Fiendish Vigor to cast False Life as an action during combat, but I honestly don't see that ever being the best option a Warlock has at 6th level or higher because they'd be giving up 2 Eldritch Blast or Pact Weapon attacks or a leveled spell (minimum 3rd level spell from Pact Magic, or a Mystic Arcanum). The opportunity cost of casting False Life at first level in combat increases significantly as you get to higher levels.
None of the other invocations are as easily outclassed or outright replaced as Fiendish Vigor. At first glance Master of Myriad Forms seems to replace Mask of Many Faces... until you realize that Alter Self requires concentration, which severely limits its usefulness by imposing an opportunity cost. No Hex or Suggestion while altered, for instance. Witch Sight similarly seems to replace Visions of Distant Realms... but you can't use Witch Sight to see places other than where you are, while the Arcane Eye spell can be moved around to see distant or hidden places. For each of these pairs of invocations, there is a genuine trade off that could be significant to gameplay. This is not the case for Fiendish Vigor because its only theoretical leg-up over the Tough Feat is that it could be cast during combat... which is basically never going to be anywhere close to the best option a Warlock has due to the incredible opportunity cost of giving up your Action for the turn. To say nothing of the fact that by Level 12, the Tough Feat essentially accounts for 2 Actions' worth of False Life casts AND you can have other THP AND the opportunity cost to cast it even once is now 3 Eldritch Blast attacks or 3 Pact Weapon attacks or a 5th Level Pact Magic cast or a 6th Level Mystic Arcanum.
Fiendish Vigor is straight up useless after a certain point in a way that the other Eldritch Invocations aren't... assuming that the RAI is that it should always be cast at 1st Level.
Looking at it from the other potential RAI perspective where the cast of False Life scales with your Pact Magic spell level because it is considered a Warlock Spell, Fiendish Vigor is suddenly much more viable. It outpaces Tough in terms of total HP until level 16, even assuming no in-combat casts, but it has the drawback of not being able to benefit from other THP sources like Dark One's Blessing, Inspiring Leader, or Rally. If you do decide to use it in combat, it's no longer the worst option in the world. 32 THP is significant, but by the time you're 16th level and fighting (presumably) roughly CR 16 creatures, you'll potentially be taking 60+ damage from an Adult Dragon's Breath Weapon. In a single turn. Using your whole Action to give yourself 32 THP is not broken at that point, but could certainly be the difference between death and survival in a non-negligible amount of situations.
In addition, other features that give a caster a spell to cast at will specify that casting at a higher level requires a higher level slot, while Fiendish Vigor does not. Examples are the Wizard's Spell Mastery and Signature Spells. This lends credence to the claim that the absence of this specification is intentional.
I believe RAI, Fiendish Vigor should scale with Pact Magic, because otherwise it is unimaginably bad in a way that none of the other Eldritch Invocations are. It's a straight-up balance issue. Where the Warlock is constrained in terms of quantity of spells it can cast, it flourishes in the flexibility and modularity it is afforded through the Eldritch Invocations. To that end, I would argue that all of the Eldritch Invocations should be viable at as many levels of play as possible.
If I were to rewrite the EI to reflect that balance and clear up confusion, the first sentence would read as "You can cast False Life on yourself at the level of your Pact Magic spell slots without expending a spell slot." If you decide that's fun for you, please steal that idea. If you decide it's not, then don't.
Fiendish Vigor should only really be replaced if you have a better form of temporary HP. Tough for 12 HP at level 6 won't go as far.
Consider you're an archfey warlock with Pact of the blade at level 6, you make three attacks using PAM and after your turn you are hit for 8 damage. You use Misty escape to cast misty step with dreadful step and move back behind the party frontliners.
After the combat you're 8 hp down, with tough that is just 8 hp gone while with fiendish vigor you just recast it and that 8thp is back at no resource cost. As a pact of the blade warlock, you're more at risk of taking damage and so that 12 thp over the course of 4 encounters could be the same as up to 48hp, tough isn't touching that.
Now as temporary HP does not stack, if you have other forms of temporary HP, such as the inspiring leader feat, that maybe where you consider getting rid of fiendish vigor.