A use for Thief of Five Fates?

[Rebonack]

The various 'you get to cast a spell once per long rest from a Warlock slot' Invocations are generally derided as some of the worst options a Warlock can take. Not only do they eat up one of your precious Invocations, they eat up a spell-slot too on top of being castable only once per day. Wizards apparently realized that this wasn't good Invocation design and we haven't seen anything similar in the various UA Invocations.

But speaking of UA Invocations, I think I may have found a combo that might make Thief of Five Fates worth picking up. Or at least might make it a not-totally-terrible option.

Maddening Hex allows the user to create a psychic disturbance around a target afflicted by curse-y Warlock features (meaning multi-classing into Bard would be a no-go) to deal Cha mod psychic damage to them and to any creatures of their choice within five feet of them. Normally this would be used along with Hex to provide the Warlock something they can consistently do with their bonus action.

HOWEVER! Thief of Five Fates targets multiple foes. So if you've got a big lump of bad guys and you Thief of Five Fates them, you can immediately follow up with Maddening Hex to transform the spell into a psychic cluster bomb. Now, this is more Invocation intensive than just grabbing Kiss of Mephistopheles if you're allowed to use UA Invocations, but if you're already picking up Maddening Hex then it might be worth trying out.

Am I reading this right? Is this the correct interpretation of these abilities?

[JellyPooga]

I think the "once/long rest" invocations get a lot of bad press, but aren't actually all that bad. UA aside, anything that expands the really rather limited Warlock spell list, even if it's only 1/long rest, is a significant boon and it's not like the spells on offer are terrible picks...

[Clone]

The invocation of Maddening Hex says "by your hex spell or by a warlock feature of yours, such as Hexblade’s Curse and Sign of Ill Omen"

Seems to me its referring to Hex or abilities rather than spells themselves.
Unless the spells from pact magic count towards such a feature, I'm not sure it'd work.
I can also see how this can be argued for it to work too, which is great for combos with the Warlock.
I like it!

[EdenIndustries]

Since the feature as written says, "As a bonus action, you cause a psychic disturbance around the target cursed by your hex spell or by a warlock feature of yours" (emphasis mine), I'd allow it. Thief of Five Fates is an Eldritch Invocation, and Eldritch Invocations are Warlock class features. As a DM I'd also allow this since you need to pick up 2 Invocations to make this work, which is a sufficient cost. It's a cool idea for sure!

[Tanarii]

The invocation of Maddening Hex says "by your hex spell or by a warlock feature of yours, such as Hexblade’s Curse and Sign of Ill Omen"

Seems to me its referring to Hex or abilities rather than spells themselves.
Unless the spells from pact magic count towards such a feature, I'm not sure it'd work.
I can also see how this can be argued for it to work too, which is great for combos with the Warlock.
I like it!
Sign of Ill Omen is another Invocation that provides a spell 1/day using a slot, just like Thief of Five Fates. So not sure what your point is. That ToFF isn't specifically refenced and SoIO is?

[Clone]

Sign of Ill Omen is another Invocation that provides a spell 1/day using a slot, just like Thief of Five Fates. So not sure what your point is. That ToFF isn't specifically refenced and SoIO is?

My mistake, I was AFB and had assumed it referred to the Hexblade ability "Shadow Hound", as it reminded me of the "Hound of Ill Omen" from the Shadow Sorcerer's level 6 ability. I was confusing doggos and thus confused the ability.

Looking at it now I see it refers to an invocation which provides a spell that causes a debuff after a failed saving throw, just like Thief of Five Fates.
After looking it over, this could be a cool interaction. Were I DMing this I'd allow it, especially since you're giving up a 3rd level spell and two invocations in order to make it happen. You COULD just fireball and save two invocations, but this is more interesting.

[Rebonack]

Looks like my thinking on this is more or less right on. It would be a pretty specialized set of invocations, but it would really allow the Warlock to double-dip in the effectiveness of those AoE save-or-suck spells.

Now here's another thought. What about using this particular combo on Mystic Arcanum that could be reasonably interpreted as a curse? Hex is the only Warlock spell that is called out as being compatible with Maddening Hex, but Mystic Arcanum don't use pact casting. They're a Warlock class feature outside pact casting just like a Hexblade's Curse is. How would you feel about, say, an upcast Hold Person as a Mystic Arcanum functioning as a focus for Maddening Hex?

Or would that be stretching it too much?

[Tanarii]

Mystic Arcanum can't be used to upcast spells, nor can they be lower level spells selected at a higher upcast level.

[Steampunkette]

I would allow it. But RAW it doesn't work.

It specifies curse within the invocation. Hex, Hexblade's Curse, and Bestow Curse all mention the word curse in their description, but Bane doesn't.

[Rebonack]

Mystic Arcanum can't be used to upcast spells, nor can they be lower level spells selected at a higher upcast level.

That seemed weird to me, but after looking into it the official word is "Not RAW, but a DM could certainly allow it." Of course, a DM could certainly allow most anything that isn't RAW. Thanks for the heads up.