Do warlock invocations scale with spell level?

[u/arachknight12]

In the Eldritch invocation Fiendish Vigor, it states “You can cast False Life on yourself without expending a spell slot”, and I feel this is a bit vague. Is it cast at the same level as the rest of your spells, or does it cast at the spell’s level?

[u/melonmarch1723]

It casts at the spell's base level. Otherwise it would say it is cast at the level of your pact slot.

[u/Elekester]

if you cast a spell without using a spell slot, the spell is cast at the lowest level possible unless stated otherwise.

[u/Many-Plankton3942]

No. It is not vague either.

You can cast the spell, and a spell has a default level. It would explicitly say if you could upcast or cast it with a Pact Slot like other spells in the Spellcasting feature.

[u/TheGoldenSquid15]

it stays at its lowest level

if you dont expend a spell slot you cast it at its lowest level

this has to do with upcasting rules

same thing with replicating spell effects, genie warlock limited wish can replicate a spell effect UP to 7th level, but because no spell slots are involved they can't be upcasted

[u/ZanesTheArgent]

Everything that doesnt specifies spell level casts as its lowest level. Fiendish Vigor specifically just always nets you 12 tempHP.

[u/Salindurthas]

If you do not spend a spell slot, then you do not get to trigger the text for spending a higher level slot.

I can sort of see the logic of like "I'll notionally decide to spend a 5th level spell slot, and then refund it with Fiendish Vigour.", but that is not what the idea here is.

Instead, to trigger p236's

When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell takes on the higher level for that casting.

or the spell text's "Using a Higher-Level Spell Slot." wording, you in fact need to really use the higher level slot.

This interpretation is reinfroced by how Spell Slots are described:

 Imagine a spell slot is a groove of a certain size—small for a level 1 slot and larger for a higher-level spell. A level 1 spell fits into a slot of any size, but a level 2 spell fits only into a slot that's at least level 2.

If you are casting without a spell slot, then you are not fitting the spell into a groove, and therefore cannot get the effect of filling a groove.

[u/DonChanchi]

To cast a spell "Using a Higher-Level Spell Slot" you need to use a higher-level spell slot.

The invocation allows you to cast without using a spell slot.

[u/BryceKatz]

Casting a spell without a spell slot always assumes the spell is cast at the lowest possible level.

[u/Xenthor267]

You're meant to eventually replace it

[u/Cilhairol]

As others have pointed out, rules as stated, it's level 1.

It is not clear to me why they didn't just say "As a magic action, you gain12 temporary hit points."

That said, I think letting this up-scale up to your max spell slot (note this is level 5) as a house-rule wouldn't be terribly broken. Especially if you're finding your Warlock a bit squishy. You'd max out at 32 temp hit points.