Does the UA warlock invocation Kiss of Mephistopheles require you to know the Fireball spell?

Unearthed Arcana: Revised Class Options includes an Eldritch Invocation option called Kiss of Mephistopheles:

Prerequisite: 5th level, the Fiend Patron, eldritch blast cantrip

You can channel the fires of Mephistopheles through your eldritch blast. When you hit a creature with that cantrip, you can cast fireball as a bonus action using a warlock spell slot. However, the spell must be centered on a creature you hit with eldritch blast.

The new UA allows the warlock to cast fireball as a bonus action — essentially building in the Sorlock in an invocation without requiring a multiclass into Sorcerer.

But the question is, do you actually need to know the fireball spell (as in, choose to have fireball take up one of your Spells Known) to be able to cast it this way?

If you use the Investment of the Chain Master Eldritch Invocation, does your familiar get a bonus to its saving throw DC from your own magic items?

The Investment of the Chain Master Eldritch Invocation states:

[…] When you cast find familiar, you infuse the summoned familiar with a measure of your eldritch power, granting the creature the following benefits: […]

[…] * If the familiar forces a creature to make a saving throw, it uses your spell save DC. […]

My question is, if the warlock has a Rod of the Pact Keeper, or Wand of the War Mage or something else which raises their saving throw DC, does the familiar inherit this when it triggers a saving throw? For example: If I had a DC 14 save with no gear and a DC 15 save with my +1 magic item, would the familiar use a 14 or a 15 for its save DC?

When does a warlock’s familiar make their attack if the warlock has the Investment of the Chain Master eldritch invocation?

So, Tasha’s Cauldron of Everything introduces a lot of new "pet" mechanics in DnD 5e. An emerging trend for some of them is that the master can take a bonus action to command the pet to take a specific action. For example:

Circle of Wildfire Druid’s Wildfire Spirit

In combat, the spirit shares your initiative count, but it takes its turn immediately after yours. The only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take another action.

Beast Master Ranger’s Primal Companion

In combat, the beast acts during your turn. It can move and use its reaction on its own, but the only action it takes is the Dodge action, unless you take a bonus action on your turn to command it to take another action.

A Pact of the Chain Warlock with the Investment of the Chain Master eldritch invocation

When you cast Find Familiar, you infuse the summoned familiar with a measure of your eldritch power, granting the creature the following benefits:

  • […]
  • As a bonus action, you can command the familiar to take the Attack action.
  • […]

While it probably won’t matter much for the Wildfire Spirit or the Primal Companion since they both take their turns on or right after the master, a familiar has its own initiative and acts on it own turn. So, if a Pact of the Chain warlock with the Investment of the Chain Master eldritch invocation uses its bonus action to command their familiar to take the Attack action, when does said familiar actually take the Attack action?
Contrast this with the base Pact of the Chain feature, where a familiar can use its reaction to take the Attack action on the master’s turn, should the master forgoes one of their attacks:

Pact of the Chain

Additionally, when you take the Attack action, you can forgo one of your own attacks to allow your familiar to use its reaction to make one attack of its own.

How does Detect Magic spell see a Warlock’s use of Devil’s Sight invocation?

I assume Eldritch Invocations are detected as magic, because they are magic:

In your study of occult lore, you have unearthed eldritch invocations, fragments of forbidden knowledge that imbue you with an abiding magical ability.

And Detect Magic spell detects magic like this:

For the duration, you sense the presence of magic within 30 feet of you. If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic, and you learn its school of magic, if any.

What does Detect Magic reveal about a visible warlock with Devil’s Sight?

I guess there are two cases: the warlock actually "seeing normally in darkness" with the invocation benefit active, and the warlock being in bright light and invocation not doing anything. Let’s leave the murky details of Devil’s sight interaction with dim light and the warlock having or not having darkvision out of scope.

Does the Voice of the Chain Master eldritch invocation let me cast a purely verbal spell through my familiar?

In D&D 5e, as a Pact of the Chain Warlock, I can choose an eldritch invocation that lets me speak in my own voice through my familiar called Voice of the Chain Master (PHB 111):

You can communicate telepathically with your familiar and perceive through your familiar’s senses as long as you are on the same plane of existence. Additionally, while perceiving through your familiar’s senses, you can also speak through your familiar in your own voice, even if your familiar is normally incapable of speech.

Healing word is a spell with only a verbal component (PHB 249):

Components: V

[…]

A creature of your choice that you can see within range regains hit points equal to 1d4 + your spellcasting ability modifier.

The description of verbal components in the rules of spellcasting (PHB 203) says the sound of my voice alone is what causes the magic of this spell to happen:

Most spells require the chanting of mystic words. The words themselves aren’t the source of the spell’s power; rather, the particular combination of sounds, with specific pitch and resonance, sets the threads of magic in motion.

Say my familiar is in another room, no matter how far away. Through my familiar’s eyes, I see a target at 60 feet. From my familiar comes my own magic-infused voice. That particular combination of sounds, with specific pitch and resonance, sets the threads of magic in motion that travel to the target and heal it.

Is this possible?

Is a signal handler invocation an upcall?

I am struggling with the definition of an upcall. Presumably, an upcall is a mechanism that allows the kernel to execute a function in userspace. By this definition, an invocation of a signal handler is an upcall because the handler runs in userspace and it is executed by the kernel. However, I noticed that upcalls are sometimes counterposed to signal handlers, without any reasonable explanations. So, is signal handler invocation an upcall, and if not, why?

Can I have a magic bow as my pact weapon without getting the Improved Pact Weapon Eldritch Invocation?

The Warlock’s Pact of the Blade feature specifies that you can only create melee weapons, but you can also turn a magic weapon into your pact weapon (without specifying that it’s only melee weapons). Can I have a magic bow as my pact weapon without getting the Improved Pact Weapon Eldritch Invocation?

Is my homebrew Eldritch Invocation that emulates the sleep spell balanced?

I’ve been inspired to make an Eldritch Invocation for warlocks that allows you to use the damage from eldritch blast, and make use of it like the dice rolled for sleep:

Eldritch Slumber

Prerequisites: eldritch blast cantrip

When you cast eldritch blast, instead of rolling 1d10 per beam, you make any spell attacks as normal and roll 2d10 per beam (plus any additional modifiers from additional abilities or critical hits). Rather than deal damage, the number rolled per beam is instead the number of hit points of creatures that beam can affect. You may target the same creature with additional beams, but the effects do not stack.

All affected creatures are rendered unconscious, until a number of rounds have passed equal to your charisma modifier, the sleeper takes damage, or someone uses an action to shake or slap the sleeper awake.

Balance Assessment

I think this is balanced because while you do not affect many creatures, you can cast it at will. At higher levels, this scales but should not past the usefulness of the original cantrip.

It also feels like where sleep affects 5d8+2d8/level, other damaging effects of the same level deal half as much damage. It stands to reason if eldritch blast deals 1d10+1d10/4 levels, sending twice as many hit points of creatures to sleep is fair, but still behind what sleep can do.

I’ve tried to word it so that you can’t stack beams together, but I don’t know if that is too big of a nerf. Also as Eldritch Blast doesn’t have a duration, I have supplied one.

Why does a character get Fate points from invocation only at the end of a scene in Fate Core?

This answer to "What happens to the fate point after a character invokes an aspect?" shows that in DFRPG (per Your Story, p. 106):

if you’re invoking an aspect on another PC or on a NPC to gain an advantage over them, that character will receive the fate point you spent, either at the end of the exchange (in conflict, see page 197) or at the end of the scene (outside of conflict).

But in Fate Core (p. 81):

if someone pays a fate point to invoke an aspect attached to your character, you gain their fate point at the end of the scene.

Why did Evil Hat change invocation so that Fate points are given out only at the end of a scene?