How can I become an invalid target for spells that target humanoids?

One of my players is a druid who would like to be able to change their creature type so that they become an invalid target against spells that target humanoids. First party WotC content (including UA) is preferred, though items from previous editions are also acceptable that can be supported by gameplay in 5e.

A spell scroll of Nystul’s Mystical Aura in D&D5e is the closest I’ve found so far by allowing the target’s creature type to be changed for divination spells, but the target is still physically its original type and may still be valid against spells targeting humanoids.

What are the dangers of renaming spells and changing their flavour, without changing mechanics at all?

I’m about to help get a bunch of interested new players into D&D, running a one-shot for them to give them a feel for the game and hopefully a fun first-taste of tabletop roleplaying.

Before starting, I’ve been asking them what kinds of things they want to get out of the game, and what their expectations are. In particular, as I’m going to pre-gen characters to simplify things, I’ve asked what kinds of character they find appealing.

However, the flavour of things that they want to play aren’t necessarily supported by the PHB – but at the same time I’d rather steer clear of homebrew as far as mechanics go. For example, one player who is interested in being “some kind of magic user that exploits darkness-like-effects”.

For an example spell: turn flaming sphere into a sphere of darkness that engulfs those it touches, absorbing the life straight from their skin. But it still does 2d6 fire damage.

I don’t plan to change damage types as this feels like a bigger can of worms. Fire-damage would still apply, but would be described as darkness eating into the target/wrapping round “like flames”. It would also mean that oil and flammable items would be affected in a similar way to fire.

That’s just one example though. Since I’d be doing this with more spells my question isn’t about one specific spell.

My question is: What dangers, if any, are there of renaming existing spells and changing their flavour text while using their existing mechanics?

Can a wizard transcribe prepared spells from multiclassing?

Say you’re a 1st-level wizard and also a 1st-level druid. Could you, as a druid, prepare spells that both classes have, like Detect Magic and Ice Knife, then, since they’re now “prepared” for you, write them in your spellbook so that you can cast them as a wizard, allowing you to cast with intelligence without needing to choose them on level-up or find them in a book/scroll?

Also, would it cost 10 gp per level or 50 gp?

As far as I can tell RAW seems to say yes but I just wanna make sure I’m not missing anything.

What would the balance implications be of removing the spell school restriction of learning spells for Eldritch Knights and Arcane Tricksters?

Both Eldritch Knights (a subclass of fighters) and Arcane Tricksters (a subclass of rogues) pull their spells from the wizard spell list, albeit in a limited way. The way in which they do this is by only being allowed to choose spells from the evocation and abjuration schools, in the case of eldritch knights, or from only choosing from illusion and enchantment, in the case of arcane tricksters. Both classes also get very small amounts of any spell they want from the wizard spell list.

How unbalanced would it be to allow both these subclasses to choose spells regardless of school from the wizard spell list? Good comparisons may include comparisons to half casters, and of course to changes in how these classes could play.

(D&D 5E) True Polymorphed Familiar Change Spells?

Say you’re a Pact of the Chain warlock, so you have a familiar with a CR of 1 or something. If you hit 17th level or find and pay a high-level mage to permanently turn your familiar into an Apprentice Wizard or LMoP’s Evil Mage, could you give it a spellbook and have it learn/prepare different wizard spells, cast rituals, etc.?

What if you get it turned into an Acolyte, could you have it prepare any first-level cleric spell, like a regular cleric could?

This is probably a ridiculous question where the answer is “if you can get a 9th-level spell then does it even matter” but I’m curious if there are any rules that point one way or the other on this.

Heightening spells

I get that I can stick a low level spell in a higher level spell slot and cast it there. My example will be Magic Missile, a 1st lvl spell. If I have the spell slot I can cast MM as a 9th level spell. No problem there.

But here’s where I’m getting lost, if I do cast MM at lvl 9, and I only use the one action to cast it, does it still only cast one missile or is it 5 missiles for 1 action? The Heightened spell section of the spell description just says

Heightened (+2) You shoot one additional missile with each action you spend.

So I’m taking that to mean for every 2 levels higher you cast it, it does that effect. If so, that would be 5 missiles for 1 action, 10 missiles for 2 actions and a full 15 if you use all 3 actions at lvl 9. Right?

And does the same kind of progression apply to cantrips? It says cantrips are automatically heightened to be cast as a spell lvl of ½ your character lvl, so at lvl 20 you’d be casting cantrips at lvl 10 power. Since the spell descriptions for heightened cantrips mostly say +1 add a die, would you be casting with the full additional 9 die or is it only one extra die period, no matter how strong its being cast?

I’m coming from 5e’s spells for dummies where it flat out tells you if your 5th lvl the spell now does this damage, if your 7th it does this now and so on, so I’m just kinda confused and don’t want to plan around a misunderstood mechanic.

Find Familiar and visual components to spells [duplicate]

This question already has an answer here:

  • Can a wizard use his familiar's senses to enlarge his “you can see” area? 1 answer

Can i use my Familiar to get past the visual components of spells as with spells like misty step that specify “A point you can see within 30 ft”?

“While your familiar is within 100 feet of you, you can communicate with it telepathically. Additionally, as an action, you can see through your familiar’s eyes and hear what it hears until the start of your next turn, gaining the benefits of any Special Senses that the familiar has. During this time, you are deaf and blind with regard to your own Senses.”

Essentially my character would be trapped in a 5×5 box with no way to see out, If my familiar was within 100 ft could I: Action see through my familiars eyes and then bonus action Misty step outside of the box?