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?

Does this magic item require that you already have the ability to use the feature that it modifies?

Last night the party was adventuring in Curse of Strahd.
In the previous session they had acquired the module-specific magic item

This item can be attuned to by a good creature. In last night’s session an NPC was able to attune to the item, unlocking its powers (emphasis mine):

Augury. You can use an action to cast an augury spell from the icon, with no material components required. Once used, this property can’t be used again until the next dawn.

Bane of the Undead. You can use the icon as a holy symbol while using the Turn Undead or Turn the Unholy feature. If you do so, increase the save DC by 2.

Cure Wounds. While holding the icon, you can take an action to heal one creature that you can see within 30 feet of you. The target regains 3d8 + 3 hit points, unless it is an undead, a construct, or a fiend. Once used, this property can’t be used again until the next dawn.

If I am reading this item correctly, anyone that can take an action can use Augury or Cure Wounds feature. The power is written in the format, ‘if you have an action, you use the action and the item grants you this ability’, even if you could not previously cast an augury or cure wounds, or even if you did not have Spellcasting ability.

However, it appears to me that what is granted by the Bane of the Undead feature is not the ability to Turn Undead, but rather a modification of that ability (+2 DC, use this as a holy symbol), to creatures that already have that feature. That is, in this sense "can use" and "can take" are granting you the ability, but "while using" requires that you already have the ability to do so. (This was important since the NPC in question did not inherently have the Turn Undead feature).

Am I interpreting this language correctly?

A good answer will show a similar example in a less ambiguous case. While this question is specifically about the 5e Curse of Strahd, I am open to an answer showing how that particular item ‘is supposed to work’ in a previous version of the module.

Does a warlock require material components for a Mystic Arcanum spell?

The description in the Warlock class says only:

At 11th level, your patron bestows upon you a magical secret called an arcanum. Choose one 6th-level spell from the warlock spell list as this arcanum. You can cast your arcanum spell once without expending a spell slot. You must finish a long rest before you can do so again.

It says nothing about having or needing the material components for the Mystic Arcanum spells. This becomes very important for spells such as Forcecage or Plane Shift.

At which point does growing plants require quintessence

In Mage the Ascension 20th Anniversary edition you need quintessence to create things from nothing. With the life sphere 3 dots (+ prime 2 dots) you can create simple life (including plants) with a point of quintessence (page 516-517 in Mage the Ascension 20th Anniversary Edition core rulebook).

With 2 dots the page 516 states:
Although he can’t yet transmute them into other states of being, he can cause flowers to bloom or wither, help trees bear fruit, and so on.
"Help a tree bear fruit" seems to imply that some limited growth also works without spending quintessence.

In the case of simple lifeforms like moss or funghi them blooming would just mean that there is more of it there afterwards since those plants mostly only grow larger.

My question is, at which point of growth would you have to use quintessence to make the plant grow larger if you use a Life 2 dot spell to bloom a patch of moss for example.

Is there precedent for this in a rulebook or is it just based on storyteller discretion?

Which spells require the caster to see a target creature or unoccupied area?

Some spells like Darkness or Fog Cloud might be used to kneecap spells that have the prerequisite phrase "that you can see" which refers either to a target creature or an unoccupied area where something might be summoned. Other spells will of course get shut down by a Silence spell, making their casting nearly impossible.

What are these spells that might get crippled or shut down completely?

Casting spells that require sight through familiar sight [duplicate]

Here is the setup:

  • I play a sorcerer and got blinded and deafened at the start of the combat
  • I use my action to use my familiar’s senses, which leaves me blinded and deafened, which I already am
  • My familiar (an owl) uses his movement and lands on my head
  • I am 10 ft away from my ally, and I want to use quickened spell to cast haste as a bonus action.

Haste states: "Choose a willing creature that you can see within range". Technically, I can’t see him with my own eyes, but I can with my familiar’s eyes which are on top of my head. In a real-world scenario, I don’t believe this would be a problem for a caster. However, my DM ruled that I can’t cast it since it strictly states that you need to see the target.

Should this be allowed?

Does Vow of Poverty require you to starve?

So, this was clearly not intended, but I’m looking back at the Vow of Poverty with a legalist’s eye, and I see the following.

To fulfill your vow, you must not own or use any material possessions, with the following exceptions: … You may carry enough food to sustain you for one day in a simple (nonmagic) sack or bag. … If you break your vow, you immediately and irrevocably lose the benefit of this feat. You may not take another feat to replace it.

It says that you must not own or use, with the following exceptions… and the exception on food is one about carrying (owning) it. As far as I can tell, no exception is given for actually allowing you to eat the food, or even take it out of the bag and hold it in your hand for an extended period of time.

I suppose that you could wait until 5th level, where the Vow itself will provide for your food needs. If you have a very good friend who is capable of casting 4th-level cleric spells, they could cast sustain on you for however long you might need to make it to 5th level. Otherwise, though, it seems that the "vow of poverty at level 1" builds may be in trouble.

Is this correct?

What action does stowing a weapon require?

The rules used to be fairly clear on this point, but they seem to have been errata’d into a more ambiguous state on this matter. Currently there doesn’t seem to be strict guidance as to what it takes to stow a held item (like a weapon), as it is no longer mentioned in the wielding item rules. However, 1st edition Core Rulebooks (such as mine) used to say it took an Interact to stow an item (this answer has a now-dated screenshot from Archive of Nethys showing the pre-errata table).

After the errata, is it clear what action it takes to stow a held item, such as a weapon?